PASTEURIZATION  OF  MILK 

FROM  THE  PRACTICAL  VIEWPOINT 


A     HANDBOOK    RELATING    TO    THE     INSTAL- 
LATION,    OPERATION     AND     CONTROL    OF 
PASTEURIZING      PLANTS.        USEFUL    TO 
MILK  DEALERS,  STUDENTS  IN    DAIRY 
SCHOOLS,  PUBLIC  OFFICIALS    HAV- 
ING   CONTROL    OF   MILK    HAND- 
LING,   AND    OF    INTEREST    TO 
THE    GENERAL   PUBLIC 


BY 

CHAS.  H.  KILBOURNE 

u 

LATE   CHIEF   OF   THE   DIVISION   OF   PASTEURIZING    PLANTS 
NEW    YORK    CITY    DEPARTMENT    OF   HEALTH 


NEW  YORK 

JOHN  WILEY   &  SONS,   INC. 

LONDON:  CHAPMAN  &  HALL,  LIMITED 

1916 


?. 
V<5 


Copyright,  1916 
BY  CHAS.  H.  KILBOUBNE 


INTRODUCTION 

In  presenting  this  book  on  the  pasteurization 
of  milk,  the  author  has  endeavored  to  so  handle 
the  subject  that  the  milk  dealers,  the  students  in 
dairy  schools,  and  health  department  officials  who 
are  charged  with  the  supervision  and  control  of 
the  milk  sold  in  their  communities,  will  find  in  the 
book  practical  assistance  in  their  work.  Except 
for  the  excellent  bulletins  issued  by  the  United 
States  Government,  there  are  few  books  which  deal 
with  the  practical  aspects  of  milk  pasteurization, 
and  the  author  felt  that  a  real  need  existed  for 
such  a  work. 

It  is  possible  that  his  long  association  with  the 
milk  work,  as  it  has  been  carried  on  by  the  New 
York  City  Department  of  Health,  has  somewhat 
colored  his  views  with  official  conservatism.  He 
has  tried,  however,  to  be  fair  and  impartial,  and  to 
look  at  matters  from  the  dealers'  point  of  view. 
He  has  presented  freely  practical  lessons  which 
iii 

358832 


INTRODUCTION 


he  has  learned  during  a  somewhat  wide  experience 
in  investigating  pasteurizing  plants. 

If  any  dealers  with  questionable  motives  look  in 
this  book  for  practical  suggestions  by  which  they 
may  be  able  to  save  milk  and  cream  which  is  going 
bad,  or  if  they  wish  to  learn  how  departmental 
regulations  can  be  evaded,  they  will  be  disap- 
pointed. 

It  is  hoped,  however,  that  dealers  who  honestly 
desire  to  handle  milk  so  that  it  will  be  safe  and 
salable  will  find  assistance  in  this  book. 

The  author  wishes  to  acknowledge  the  assistance 
and  good  advice  which  he  has  received  from  Dr. 
Wm.  H.  Park,  Dr.  Chas.  F.  Boldune,  Ole  Salthe 
and  James  E.  Thomson,  and  from  Inspectors 
Ryan,  Lee  and  others  in  the  New  York  City  De- 
partment of  Health.  Also  he  wishes  to  thank  the 
various  manufacturers  of  dairy  machinery  for  in- 
formation given  and  illustrations  supplied. 

C.  H.  K. 

New  York,  September  1,  1916. 
iv 


The  Pasteurization  of  Milk  from  the 
Practical  Viewpoint 

CHAPTER    I 

PASTEURIZATION    IN    GENERAL 

The  guarding  of  food  supplies  in  large  towns 
and  cities  is  one  of  the  most  important  functions  of 
government  activity.  This  activity,  like  all  forms 
of  organized  effort,  has  been  a  gradual  develop- 
ment. In  the  most  primitive  communities,  individ- 
uals naturally  felt  a  certain  care  over  the  food 
which  they  ate.  This  interest  was  instinctive  and 
fundamental,  since  each  individual  was  conscious 
that  some  foods  were  dangerous.  He  therefore 
obeyed  the  law  of  self-preservation  when  he  se- 
lected his  food. 

As  the  homes  of  individuals  became  more  con- 
gested on  account  of  the  increase  in  population, 
it  grew  to  be  increasingly  difficult  for  the  indi- 
vidual to  select  the  food  which  he  ate.  He  there- 
fore came  to  depend  more  and  more  upon  the 
judgment  of  other  people  who  had  either  used 
similar  food  before  or  else  knew  how  it  was  pro- 
1 


THE.  PAST^U^^ATJON    OF    MILK 

duced.  The  substitution  of  the  judgment  of  oth- 
ers for  his  own  personal  inspection  of  food  nat- 
urally developed  into  a  certain  sort  of  communal 
or  public  control  of  foods.  As  communities  be- 
came more  and  more  congested,  it  became  neces- 
sary to  centralize  the  control  of  foods  under  some 
definite  organization.  This  centralized  control, 
which  was  usually  at  first  vested  in  some  private 
organization,  was  later  taken  over  by  the  govern- 
ment which  obtained  in  the  town  or  city.  Thus  we 
have  the  Boards  of  Food  Control,  which  are  now 
usually  centered  in  the  Health  Departments. 

As  the  inter-dependence  of  the  various  towns  and 
cities  became  more  fully  recognized,  it  became  evi- 
dent that  not  only  the  cities  but  the  states  should 
on  broad  lines,  regulate  the  production  and  sale  of 
foods.  This  state  regulation  of  foods  has  been  cen- 
tered partially  in  State  Health  Departments,  partly 
in  the  Agricultural  Departments  and  sometimes  in 
special  departments  whose  duties  have  been  to 
control  the  foods  sold  in  the  state.  These  state 
departments  are  becoming  increasingly  efficient  as 
the  good  work  which  they  do  is  becoming  more  and 
more  recognized. 

Since  the  means  of  communication  and  transpor- 
2 


FROM    THE    PRACTICAL    VIEWPOINT 

tation  are  becoming  more  rapid,  the  effect  is  that 
the  world  is  becoming  smaller,  and  so  the  consump- 
tion of  foods  is  not  confined  to  the  states  where  it 
is  produced.  The  increasing  use  of  cold  storage 
facilities  for  preserving  foods  also  adds  to  the  wide 
area  from  which  cities  and  towns  can  obtain  the 
foods  which  are  there  consumed.  It,  therefore, 
becomes  evident  that  state  regulation  is  too  narrow. 
In  order  to  properly  protect  the  citizens,  therefore, 
the  general  government  has  taken  up,  to  a  large 
extent,  the  control  of  foods  which  enter  into  inter- 
state commerce,  and  government  standards  are 
adopted. 

Among  the  articles  of  food  which  have  perhaps 
received  the  largest  share  of  attention  we  find  milk. 
This  attention  has  been  deserved  on  account  of  the 
almost  universal  use  of  milk,  and  also  on  account 
of  the  fact  that  it  becomes  easily  infected  with 
dangerous  bacteria,  and  having  become  infected  it 
is  itself  an  ideally  good  medium  for  their  growth. 
The  milk  thus  becomes  so  changed  or  decomposed 
that  it  is  frequently  unsafe  for  food.  The  oppor- 
tunities for  infection  are  many,  on  account  of  the 
many  persons  through  whose  hands  it  passes  be- 
fore it  reaches  the  city  consumer,  and  where  it  is 
3 


THE    PASTEURIZATION    OF    MILK 

perhaps  fed  to  the  children  who  depend  upon  milk 
for  their  life.  At  any  point  along  the  line  of 
travel  from  the  cow  to  the  consumer  it  may  be- 
come dangerously  infected.  If  the  cows  from 
which  it  is  drawn  are  not  healthy,  the  milk  may 
start  on  its  journey  in  an  unsafe  condition.  Even 
if  it  is  perfectly  wholesome  when  drawn  from  the 
cows,  it  may  at  any  point  along  its  line  of  travel 
become  changed  from  its  natural  state. 

Disease-producing  bacteria  or  other  less  harm- 
ful germs  may  enter  the  milk  from  stable  dust  or 
from  the  manure  and  urine  which  drops  from  the 
cow  herself.  The  milk  bottles  and  cans  may  have 
been  carelessly  washed  or  the  water  with  which 
the  washing  is  done  may  be  from  contaminated 
sources.  Diseased,  or  unclean  persons  may  be  em- 
ployed in  milking  the  cows,  or  in  handling  the 
milk  after  it  is  drawn.  Cans  or  bottles  in  which 
the  milk  is  placed  may  have  been  returned  from 
the  consumer  in  filthy  condition  and  have  been 
again  used  for  containing  fresh  milk  before  being 
thoroughly  washed  and  sterilized.  Contagious  dis- 
ease may  have  been  in  the  homes  from  which  they 
are  returned. 

Much  of  the  milk  in  large  cities  is  handled  at 
4 


FROM    THE    PRACTICAL    VIEWPOINT 

creameries  or  shipping  stations  which  are  located 
in  the  country  and  from  which  the  milk  is  shipped 
to  the  cities.  Thus,  there  is  an  added  opportu- 
nity for  milk  infection  on  account  of  the  insani- 
tary buildings  or  from  coming  in  contact  with 
dust-laden  air  or  diseased  employees.  Once  hav- 
ing gained  access  to  the  milk  the  growth  and  mul- 
tiplication of  the  germs  is  aided  by  the  powerful 
agencies  of  age  and  heat.  If  germs  which  pro- 
duce disease  get  into  the  milk  the  danger  that  epi- 
demics of  disease  will  occur  is  a  serious  one.  Each 
point  in  the  handling  of  milk  is  therefore  an  im- 
portant point,  for  the  chain  of  milk  safety  is  only 
as  strong  as  its  weakest  link. 

Aside  from  the  danger  of  bacterial  contamina- 
tion  there  is  of  course  the  possibility  of  actual 
adulteration  being  practised  within  the  legal  defini- 
tion of  that  term.  Foreign  substances  may  be 
added,  such  as  water,  coloring  matter,  preserva- 
tives, etc.,  or  the  cream  may  be  removed.  Such 
adulteration  may  be  accidental  or  it  may  be  de- 
liberately practised,  with  "malice  aforethought," 
with  intent  to  deceive  and  defraud  the  final  con- 
sumer, for  the  purpose  of  increasing  the  profits. 
On  account  of  the  sharp  competition  which  ex- 
5 


THE    PASTEURIZATION    OF    MILK 

ists  in  modern  trade,  some  dealers  consider  that 
they  are  justified  in  doing  some  things  which  are 
objected  to  by  public  boards  of  control.  Some- 
times milkmen  will  endeavor  to  save  a  perishable 
product  by  the  use  of  preservatives.  This  form  of 
adulteration,  however,  is  at  present  very  little 
practised. 

The  importance  which  attaches  to  the  public  or 
communal  control  of  milk  is  not  the  only  force 
which  is  lifting  to  a  higher  level  the  character  of 
the  milk  sold  to  the  public.  Milk  dealers  them- 
selves are  realizing  more  and  more  that  modern 
conditions  are  such  that  only  the  best  and  the 
most  efficiently  produced  and  handled  product  can 
remain  in  the  market.  They  are  therefore  be- 
coming more  and  more  active  in  establishing 
means  for  effectively  controlling  their  own  sup- 
plies. The  methods  employed  are  various.  Asso- 
ciations of  men  have  been  formed,  the  object  of 
which  is  to  secure  mutually  useful  advice  and  to 
give  each  other  the  benefits  of  individual  expe- 
riences. 

The  larger  dealers  establish  within  their  own 
organizations  an  efficient  inspection  service  and 
seek  by  means  of  laboratory  tests  and  research 
6 


FROM    THE    PRACTICAL    VIEWPOINT 

work  to  study  their  problems  and  so  secure  the 
best  milk  possible  at  the  least  expense,  and  with 
the  least  amount  of  waste.  Thus  the  governmen- 
tal forces  and  the  dealers  themselves  both  work 
toward  the  goal  of  a  better  milk  supply. 

The  great  importance  of  the  problems  which  * 
affect  the  securing  of  a  safe  milk  supply  has  led 
to  the  publication  of  many  books,  in  which  the  va- 
rious phases  of  the  matter  have  been  considered. 
The  composition  of  the  milk,  its  chemical  charac- 
teristics, the  number  and  kind  of  bacteria  con- 
tained, the  forms  of  adulteration  which  occur  and 
the  methods  for  detecting  such  adulteration  have 
all  been  broadly  covered.  The  relation  of  milk  to 
the  public  health  and  the  disease  epidemics  which 
have  been  due  to  infected  milk  have  received  large 
attention  in  published  works.  Much  has  also  been 
published  regarding  the  most  effective  methods  to 
be  employed  in  the  public  control  of  milk  supply. 

While  there  is  an  extensive  literature  concern- 
ing the  problems  of  milk  pasteurization  dealing 
with  the  matter  from  the  theoretical  side,  and  also 
covering  certain  special  phases  of  the  work,  it  is 
rather  surprising  to  find  how  little  of  this  is 
available  for  the  practical  use  of  the  milkman  who 

7 


THE    PASTEURIZATION    OF    MILK 

wishes  to  install  pasteurizing  apparatus  and  to  so 
handle  his  output  that  the  most  efficient  service 
can  be  secured  with  the  least  possible  expense. 
This  dearth  of  literature  has  been  no  doubt  largely 
due  to  the  fact  that  the  information  which  the 
many  practical  men  have  gained  in  their  experi- 
ments has  never  been  so  brought  together  that  it  is 
available  for  the  use  of  those  who  are  seeking 
knowledge  along  practical  lines.  That  this  should 
be  so  is  but  natural,  for  several  reasons. 

First:  The  manufacturers  who  are  interested  in 
emphasizing  the  good  points  of  their  apparatus 
are  not  inclined  to  call  attention  to  their  defects. 

Second:  Milk  dealers  who,  through  experiments 
in  trying  out  various  forms  of  apparatus  have 
learned  what  appears  to  be  best  suited  to  their 
needs,  are  not  inclined  to  publish  to  the  world 
information  which  has  cost  them  much  time  and 
money  to  secure.  Should  they  do  so,  they  would 
be  benefitting  their  competitors. 

Third:  Public  officials  in  city,  state  or  national 
public  service,  who  have  made  many  inspections, 
conducted  tests  and  carried  on  extensive  research 
work  are  comparatively  few.  In  fact,  in  very  few 
cities  is  the  field  for  observation  sufficiently  exten- 
8 


FROM    THE    PRACTICAL    VIEWPOINT 

sive  to  enable  such  officials  to  draw  unbiased  or 
broad  conclusions.  State  officials  are  as  yet  doing 
little  work  along  these  lines.  The  general  govern- 
ment has  been  and  is  now  carrying  on  extensive 
and  valuable  experimental  work,  and  as  a  result 
much  useful  and  valuable  information  has  been 
published.* 

The  writer  has  published  some  matter  which  his 
experience  has  taught  him.f  Dr.  Rosenau  has 
devoted  considerable  space  to  the  subject  of  milk 
pasteurization  and  has  given  much  valuable  infor- 
mation on  the  subject.^ 

Additional  information  which  is  of  considerable 
value  has  been  acquired  by  the  experience  of  the 
writer  and  other  inspectors  in  the  New  York  City 
Department  of  Health,  working  in  conjunction 
with  the  laboratories.  It  seems  to  be  proper  that 
this  information  could  be  available  to  the  general 
public. 

As  before  stated,  the  application  of  heat  to  per- 
ishable foods  in  order  to  preserve  them  from  de- 


*Ayers  and  Johnson,  Bureau  of  Animal  Industry — Circular 
184  and  other  publications. 

fN.  Y.  C.  Department  of  Health  Reprint  Series  Nos.  1  and  27. 
tThe  Milk  Question  by  M.  J.  Rosenau. 

9 


THE    PASTEURIZATION    OF    MILK 

cay  has  probably  been  practised  since  the  discov- 
ery of  fire.  The  earliest  record  of  the  application 
of  heat  to  food  in  a  scientific  way  was  in  1872, 
when  Sheele,  the  well-known  Swedish  chemist, 
discovered  that  vinegar  could  be  preserved  against 
spoiling  by  heating  it.  Soon  after  this  other  peo- 
ple began  to  preserve  fruits,  vegetables,  milk,  etc., 
v/  by  heating  them  in  closed  vessels.  No  scientific  ex- 
planation, however,  of  the  reason  why  the  heating 
process  preserves  these  foods  appeared  until  I860 
to  1870,  when  Pasteur,  in  his  studies  as  to  the 
causes  for  the  deterioration  which  took  place  in 
wines  and  beers,  discovered  that  there  was  certain 
forms  of  life  previously  unknown  whose  unchecked 
growth  gave  to  liquor  its  bad  flavors,  etc.  These 
were  termed  by  Pasteur  "diseases."  He  discovered 
that  by  heating  beer  and  wine  to  a  temperature  of 
158°  to  176°  F.,  and  holding  the  fluids  at  these 
temperatures  for  a  period  of  time,  the  "disease 
germs,"  as  he  called  them,  were  destroyed  and  the 
flavor  of  the  liquor  was  improved,  the  loss  by 
spoiling  being  at  the  same  time  prevented. 

This  discovery  was  of  immense  financial  benefit 
to  Europe,  and  in  consequence  the  heating  of  wines 
and   beers    became    very    generally    practised,   the 
10 


FROM    THE    PRACTICAL    VIEWPOINT 

process  being  termed  "pasteurization,"  from  the 
name  of  the  man  who  originated  it.  At  the  present 
time,  no  brewery  is  considered  to  be  wrell  equipped 
and  up  to  date  unless  extensive  apparatus  is  em- 
ployed to  heat  the  product  before  it  is  placed  upon 
the  market. 

The  thought  that  the  same  principle  might  be 
applied  to  the  preservation  of  milk  on  an  exten- 
sive scale  had  its  birth  in  Europe,  and  it  is  claimed 
that  the  first  commercial  milk  pasteurizer  was 
made  by  Ahlborn  in  Hildeshein,  Germany,  in  1880, 
and  that  a  similar  apparatus  was  made  in  the  same 
year  by  Fresca  in  Berlin,  Germany.  The  process 
was  later  adopted  in  Denmark,  where  dairying  has 
reached  such  a  high  degree  of  perfection. 

At  all  events,  the  machine  now  known  as  the 
Danish  pasteurizer  was  introduced  into  this  coun- 
try by  Reid  about  1895,  and  is  now  sold  under 
various  names  by  different  manufacturers.  Modi- 
fications and  developments  of  the  original  idea 
form  the  basis  of  nearly  all  the  pasteurizing  ma- 
chines used  at  the  present  time. 

This  form  is  illustrated  in  Figs.  1  and  2,  and  is 
described  more  in  detail  later  in  this  book. 

In  Denmark  the  object  sought  by  the  use  of  the 
11 


THE    PASTEURIZATION    OF    MILK 

pasteurizer  was  the  improvement  of  the  flavor  and 
quality  of  butter,  the  manufacture  of  whicli  is  such 
an  important  industry  in  that  country.  The  pas- 
teurization of  the  cream  used  for  butter  is  there 
generally  practised,  and  it  is  subsequently  ripened 
by  the  introduction  of  a  pure  culture  grown  in  the 
laboratories  in  order  to  secure  the  most  desirable 
texture  and  flavor.  These  methods  have  resulted 
in  the  production  of  a  butter  in  Denmark  which  is 
considered  to  be  a  standard  article.  The  indus- 
try has  grown  remarkably  and  its  products  are 
shipped  to  England  and  other  parts  of  Europe  in 
normal  times,  and  have  also,  in  times  of  shortage, 
been  shipped  to  the  United  States. 

When  it  became  appreciated  in  Denmark  that 
the  spread  of  bovine  tuberculosis  was  a  danger- 
ous menace  to  the  dairy  industry,  a  law  was  passed 
requiring  that  milk  whey,  etc.,  which  was  fed  to 
calves,  swine  and  other  animals  must  be  heated 
before  being  fed  in  order  to  prevent  the  spread  of 
this  disease  among  the  growing  stock.  This 
proved  so  useful  in  accomplishing  its  object,  that 
similar  laws  have  been  passed  in  various  states  in 
this  country.  Vermont  and  Pennsylvania  have 
such  laws  in  the  East.  Strange  to  say,  many  of 
12 


FROM    THE    PRACTICAL    VIEWPOINT 

the  dairymen  object  to  this,  much  preferring  the 
unheated  skim  milk.  The  dangers  are  not  gen- 
erally appreciated. 

It  became  apparent  to  some  people  that  that 
which  was  good  for  preventing  disease  among  cat- 
tle would  also  be  useful  in  preserving  health 
among  children,  and  in  1866  Soxhlet  advocated  that 
milk  which  was  fed  to  infants  be  heated.  About 
this  time,  Jacobi,  the  distinguished  American  pedi- 
atrist,  advised  the  boiling  of  milk  fed  to  infants. 
In  1869  he  referred  to  the  apparatus  devised  by 
Soxhlet,  this  being  the  first  American  reference 
to  the  subject.  This  was  before  it  was  so  well 
known,  as  is  now  generally  accepted,  that  milk  is 
a  means  of  carrying  infectious  diseases,  such  as 
diphtheria,  typhoid,  scarlet  fever,  etc.  Jacobi  found 
that  children  fed  upon  boiled  milk  were  less  liable 
to  have  intestinal  disorders,  and  his  long  and  con- 
tinued success  in  treating  children  tends  to  dis- 
credit the  assertions  made  by  some  that  the  pas- 
teurization of  milk  at  comparatively  low  tempera- 
tures destroys  its  nutritive  value  and  is  injurious 
to  children.  Jacobi  still  advocates  the  boiling  of 
milk. 

It  was  soon  brought  to  the  attention  of  milk 
13 


THE    PASTEURIZATION    OF    MILK 

dealers  that  milk  which  was  old  and  liable  to  be- 
come a  commercial  loss  on  account  of  souring 
could  be  saved  if  it  were  heated,  and  that  the  fer- 
mentation due  to  the  growth  of  the  enormous  num- 
ber of  bacteria  in  milk  could  thus  be  checked. 
Milk  which  had  been  handled  in  an  unclean  man- 
ner, or  which  had  been  badly  cooled  by  insuffi- 
cient icing,  or  which  it  became  necessary  to  hold 
for  a  long  time  before  sale,  could  still  be  made 
marketable  by  rapidly  heating  and  cooling  it.  Lit- 
tle attention,  however,  was  paid  to  the  matter  of  a 
uniform  heating  of  the  milk,  or  to  the  exact  degree 
of  temperature  to  which  it  was  subjected.  Almost 
no  attention  was  directed  to  the  destruction  of 
pathogenic  bacteria.  These,  in  fact,  were  little  un- 
derstood by  the  milk  dealers,  and  few  dealers  main- 
tained laboratories  for  studying  milk  problems. 

On  account  of  the  questionable  motives  which 
actuated  dealers  in  adopting  this  method  of  milk 
treatment,  as  well  as  the  faulty  methods  employed, 
health  authorities,  as  a  rule,  at  first  looked  upon 
the  pasteurization  of  milk  with  disfavor.  It  was 
considered  that  the  process  was  a  makeshift  and 
simply  used  as  a  means  of  covering  up  bad  prac- 
tices in  the  production  and  handling  of  milk.  In- 
14 


FROM    THE    PRACTICAL    VIEWPOINT 

stead  of  encouraging  the  pasturization  of  milk,  or 
even  ignoring  it,  health  authorities  rather  took 
steps  to  discourage  its  practice.  The  desire  to  se- 
cure a  safe  milk  supply  for  the  public  took  form 
in  strenuous  efforts  to  clean  up  the  sources  from 
which  the  milk  was  secured,  to  secure  proper  re- 
frigeration and  to  assure  clean  handling.  The  cry 
was  for  clean  milk  as  produced  from  the  dairies, 
and  the  process  of  pasteurization  was  frowned 
upon. 

In  New  York  and  other  cities,  commendable 
progress  was  made  in  the  effort  to  secure  a  clean, 
safe  raw  milk,  and  the  improvement  made  in  the 
conditions  under  which  milk  is  handled,  particu- 
larly in  receiving  stations  and  creameries,  can 
hardly  be  appreciated  by  those  who  were  unfa- 
miliar with  conditions  before  the  campaign  for 
clean  milk  was  inaugurated.  Dairy  conditions 
have  also  been  greatly  improved,  and  the  dairymen 
themselves  repeatedly  say  that  they  would  not  for 
any  consideration  go  back  to  old  conditions.  All 
efforts  made  to  advance  the  production  of  clean 
milk  should  be  continued  with  unabated  vigor. 

It  soon  became  apparent,  however,  that  the  se- 
curing for  a  large  city  of  a  raw  milk  supply 

15 


THE    PASTEURIZATION    OF    MILK 

which  could  be  guaranteed  to  be  reasonably  clean 
and  safe  was  practically  impossible.  If  it  was  se- 
cured, it  would  involve  the  expenditure  of  an  enor- 
mous amount  of  money  and  energy,  which  the  tax- 
payers would  not  approve,  and  it  was  seen  that  it 
might  result  in  so  much  added  expense  to  pro- 
ducers and  dealers  that  the  price  of  milk  to  the 
consumer  would  be  greatly  increased,  perhaps  to 
such  an  extent  that  the  sale  of  this  valuable  uni- 
versal food  would  be  seriously  curtailed. 

Public  health  administrators  were  at  length  led 
to  the  conclusion  that  the  pasteurization  of  milk 
was  the  only  practical  means  of  securing  a  sup- 
ply which  would  be  reasonably  safeguarded  against 
dangerous  infection.  By  many  persons  it  was  con- 
sidered to  be  a  makeshift,  and  it  is  still  so  re- 
garded by  some  authorities,  it  being  held  by  them 
that  its  employment  should  only  be  continued  until 
a  clean,  safe  raw  supply  can  be  secured.  Others, 
and  by  far  the  majority  of  authorities,  are,  how- 
ever, convinced  that  pasteurization  will  always  be 
a  necessity,  and  that  even  the  best  of  raw  milk 
should  be  provided  with  the  additional  safeguard 
which  will  be  secured  by  pasteurization. 

It  is  even  urged  by  some  that  certified  milk, 
16 


FROM    THE    PRACTICAL    VIEWPOINT 

which  is  the  safest  raw  milk  possible  to  be  ob- 
tained, should  be  pasteurized  before  being  used  for 
infant  feeding.  This  thought  has  been  strength- 
ened by  information  of  comparatively  recent  dis- 
covery, that  milk  may  become  infected  through 
coming  in  contact  with  persons  who  harbor  dis- 
ease germs,  but  who  are  not  in  any  way  ill.  These 
persons  are  therefore  perfectly  innocent  of  any 
knowledge  that  they  are  a  source  of  infection  to 
milk,  and  thus  a  dangerous  and  insidious  menace 
to  the  milk  consumer.  It  has  been  found  that  cer- 
tain persons  may  be,  and  not  infrequently  are,  in- 
fected with  typhoid  bacilli,  without  they  themselves 
knowing  that  they  are  thus  infected.  Such  per- 
sons are  known  as  typhoid  carriers.  Other  persons 
harbor  the  germs  of  diphtheria  in  mouth  and 
throat,  without  having  any  symptoms  of  the  dis- 
ease whatever.  Such  persons  may  handle  milk  and 
unwittingly  infect  it. 

Within  the  last  few  years  there  have  been  in 
different  cities  epidemics  of  septic  sore  throat. 
These  have  occurred  in  Boston,  Baltimore,  Chi- 
cago, etc.  In  Boston  in  1911  several  thousand 
persons  were  made  ill  by  milk  coming  from  a 
farm  where  the  milk  was  exceptionally  well  cared 

17 


THE    PASTEURIZATION    OF    MILK 

for.*  Many  of  the  persons  thus  affected  died. 
In  1912  a  similar  epidemic  occurred  in  Baltimore, 
where  many  persons  were  made  sick  and  many 
deaths  occurred.  This  was  traced  to  milk  infec- 
tion, f  Had  these  milks  been  properly  pasteur- 
ized, these  epidemics  of  disease  would  probably 
have  been  avoided. 

Aside  from  the  foregoing  considerations,  the 
fact  that  a  very  considerable  percentage  of  cows 
producing  milk  are  tuberculous  gives  an  added 
reason  why  it  is  desirable  to  heat  the  milk  be- 
fore use.  There  has  been  much  misapprehension 
in  the  public  mind  regarding  the  actual  danger 
which  threatens  human  beings  from  this  source. 
There  seems  to  be  no  doubt  that  these  dangers, 
while  real,  have  been  somewhat  exaggerated.  In 
the  first  place,  the  fact  that  a  cow  may  be  seri- 
ously affected  with  tuberculosis  does  not  make  it 
certain  that  her  milk  is  dangerous  to  use.  If 
proper  care  is  exercised  while  the  milk  is  being 
drawn  from  the  cow,  none  of  the  germs  will  get 


*Winslow,  C.  E.  A.,  Journal  of  Infectious  Diseases,  Volume  X 

No.  1,  January,  1912. 

fPublic  Health  Reports,  November  22,  1912. 

18 


FROM    THE    PRACTICAL    VIEWPOINT 

into  the  milk.  Of  course,  if  the  disease  existed  in  the 
udder  of  the  cow,  or  in  the  milk  ducts,  there  would 
then  be  direct  contamination  of  the  milk  as  it  was 
drawn.  Cows  more  frequently,  however,  have  the 
disease  in  the  lungs  or  other  parts  of  the  body,  in 
which  case  the  germs  will  pass  through  the  alimen- 
tary tract  and  be  voided  with  the  urine  and  faeces. 
If  the  cows  are  allowed  to  become  badly  soiled, 
particles  of  manure  and  dirt,  carrying  with  them 
the  tubercle  bacilli,  will  inevitably  fall  into  the 
milk,  thus  infecting  it.  It  is  also  possible  that 
dried  manure  in  stables  where  tubercular  cattle 
are  kept  will  produce  dust,  which,  when  stirred 
up  by  the  movements  of  the  cattle  or  by  persons 
and  by  sweeping,  may  fall  into  the  milk.  This 
danger  is  probably  more  imaginary  than  real, 
since  recent  experiments  by  the  Geneva  Experi- 
ment Station  *  indicate  that  stable  dust  plays  a 
part  in  milk  infection  which  is  of  comparatively 
little  importance.  It  is  also  true  that  the  exposure 
of  manure  to  light  and  air  for  a  length  of  time 
sufficient  to  produce  a  dry  dust  would  tend  to  de- 
stroy the  tubercle  bacilli.  The  amount  of  infec- 


*Bul.  409.  N.  Y.  Ag.  Exp.  Sta. 
19 


THE    PASTEURIZATION    OF    MILK 

tion  would  be  therefore  comparatively  small.  It 
is  also  a  known  fact  that  while  tubercle  bacilli  will 
live  in  milk,  they  will  not  multiply. 

The  apprehension  experienced  by  many  persons 
that  they  may  be  infected  with  tuberculosis  from 
the  milk  which  they  consume  should  be  lessened 
by  their  knowledge  of  this  further  fact,  namely, 
that  tuberculosis  of  the  bovine  type  with  which 
cattle  are  affected  is  rarely  infectious  to  human 
beings  who  are  over  fifteen  years  of  age,  and 
rarely  causes  fatal  tuberculosis  in  children  over 
five  years  old.  The  careful  examination  of  hun- 
dreds of  cases  where  death  has  occurred  from 
tuberculosis  among  children  appears  to  conclu- 
sively show  that  the  danger  of  infection  from  bo- 
vine tuberculosis  is  largely  limited  to  persons 
under  fifteen  years  of  age.  Of  deaths  from  tuber- 
culous affections  of  persons  under  this  age,  only 
10  per  cent,  had  tuberculosis  of  the  bovine  type. 
This  has  been  determined  for  New  York  City  by 
investigations  carried  on  by  Park  and  his  col- 
leagues, extending  over  several  years,  and  the  same 
conclusions  have  been  reached  by  European  sci- 
entists. 

The  records  of  New  York  City  for  the  years 
20 


FROM    THE    PRACTICAL    VIEWPOINT 

1Q13-1914-1915    show    the    following    interesting 
facts: 

DEATHS  OF  CHILDREN  UNDER  FIFTEEN  YEARS. 

1913  1914  1915 

From  all  causes...    23,574        22,312        23,031 
From  all  tubercular 

diseases    1,288  1,166  1,200 

10  per  cent  of  these 
latter  figures  in- 
dicate    128.8  116.6  120. 

These  represent  the  number  of  persons  who  died 
in  these  years  from  tuberculosis  which  was  prob- 
ably of  bovine  type. 

This  means  that  out  of  every  1,000  deaths  from 
all  causes  of  children  under  fifteen  years  of  age, 
5.4  in  1913,  4.8  in  1914,  and  5.2  in  1915,  had 
tuberculosis  which  was  probably  of  the  bovine 
type. 

While  it  is  possible  that  bovine  tuberculosis  may 
reach  human  beings  through  infected  meat  or  by 
direct  infection  from  dust,  dirt,  etc.,  it  is  probable 
that  most  of  it  is  due  to  infected  milk. 

There  are  many  cases  of  tuberculosis  existing 
21 


THE    PASTEURIZATION    OF    MILK 

in  bones  and  glands  which  do  not  result  fatally. 
Nearly  one-half  of  these  are  thought  to  be  of  the 
bovine  type,  and  very  likely  have  their  origin  in 
milk. 

It  is  evident,  therefore,  that  while  the  danger  of 
tubercular  infection  from  milk  when  expressed  in 
terms  of  percentages  is  comparatively  slight,  there 
appears  to  be,  nevertheless,  a  definite  danger  to 
children  from  this  source,  and  the  safeguarding  of 
this  milk  by  pasteurization  is  extremely  desirable. 

Rosenau  *  places  tuberculosis  first  among  the 
diseases  carried  by  milk,  thus  considering  it  a 
greater  menace  than  typhoid  fever. 

All  these  facts  have  induced  most  health  authori- 
ties to  change  their  attitude  toward  the  pasteuriz- 
ing of  milk  for  general  use,  and  it  is  now  the  ex- 
ception instead  of  the  rule  to  find  persons  familiar 
with  the  subject  who  favor  the  use  of  raw  milk, 
except  when  it  is  from  dairies  which  are  abso- 
lutely above  suspicion. 

The  important  consideration  which  influences 
authorities  when  they  insist  that  milk  be  pasteur- 
ized is  of  course  the  desire  that  the  milk  may  be 
free  from  dangerous  bacteria. 

*The  Milk  Question — M.  J.  Rosenau. 
22 


FROM    THE    PRACTICAL    VIEWPOINT 

There  are  commercial  reasons  which  influence 
dealers,  such  as  the  desire  to  prevent  the  souring, 
and  thus  the  loss  of  milk,  but  these  considerations 
have  little  weight  with  health  authorities.  The 
prevention  of  economic  waste  of  food  products  has 
a  bearing  upon  the  public  health,  and  there  are 
indications  that  the  personal  interest  which  those 
in  authority  have  as  men  in  these  matters  is  being 
extended  to  their  official  interest.  Care  must  be 
observed,  however,  that  these  two  considerations  be 
justly  balanced. 

The  United  States  Government  has  endeavored 
to  reduce  the  losses  which  result  from  the  condem- 
nation of  cream  which  is  not  considered  fit  to  use 
as  cream.  This  is  accomplished  by  partially  de- 
naturing it  by  the  addition  of  salt,  so  that  it  can  be 
used  for  butter  making.  An  attempt  has  also  been 
made  to  prevent  the  destruction  of  milk  which  has 
a  temperature  above  that  fixed  by  the  authorities 
as  legal.  It  is  well  known  that  in  some  cities  this 
drastic  action  is  taken  in  order  to  secure  proper 
refrigeration.  Such  destruction  of  milk,  which  has 
a  high  food  value,  should  be  looked  upon  as  almost 
criminal. 

Careful  experiments  carried  on  by  Park,  Rose- 


THE    PASTEURIZATION    OF    MILK 

nau,  and  others  have  demonstrated  the  fact  that 
if  milk  is  heated  to  a  temperature  of  140°  F.,  and 
is  held  at  this  temperature  for  twenty  minutes,  or 
even  less,  all  of  the  pathogenic  or  disease-produc- 
ing bacteria  will  be  destroyed.  Also,  if  the  milk 
is  heated  to  a  uniform  temperature  of  158°  F., 
and  held  thereat  for  one  minute,  all  such  disease 
germs  will  be  killed.  Between  these  extremes,  dif- 
ferent degrees  of  temperature,  and  correspond- 
ingly varying  lengths  of  holding  time,  will  pro- 
duce equally  good  results.  These  experiments 
have  been  carried  on  of  course  in  laboratories 
where  ideal  conditions  for  securing  accurate  re- 
sults existed.  Accurate  temperatures  could  be  ob- 
tained and  the  length  of  time  for  which  the  milk 
was  held  could  be  carefully  controlled.  When, 
however,  pasteurization  is  carried  on  under  com- 
mercial conditions,  where  large  quantities  of  milk 
are  handled,  the  same  amount  of  accuracy  is  not 
possible.  There  are  variations  in  temperature  and 
variations  in  the  length  of  time  for  which  it  is 
held,  due  largely  to  the  mechanical  defects  or 
limitations  in  all  forms  of  machinery.  These  fac- 
tors of  error  render  the  results  uncertain,  and  it 
is  therefore  desirable  that  the  temperatures  and 
24 


FROM    THE    PRACTICAL    VIEWPOINT 

the  lengths  of  time  for  holding,  which  in  the  labo- 
ratory tests  have  been  found  to  be  effective,  be 
somewhat  increased,  in  commercial  practice. 

Various  cities  have  made  regulations  in  this  re- 
spect which  appear  to  best  suit  local  conditions. 
In  New  York  City,  when  regulations  were  first 
adopted  concerning  milk  pasteurization,  the  length 
of  time  for  which  milk  must  be  held  when  heated 
to  158°  F.  was  officially  fixed  at  no  less  than  three 
minutes,  and  if  heated  to  140°  it  must  be  held  for 
at  least  twenty  minutes.  Between  these  extremes 
of  temperature  holding  times  were  fixed  which  va- 
ried between  three  minutes  and  twenty  minutes. 

Experiments  were  made  by  Schores  and  Rose- 
nau  *  in  which  careful  tests  were  carried  on  while 
milk  was  being  pasteurized  in  the  ordinary  way, 
a  commercial  pasteurizer  and  holding  device  being 
used.  These  tests  were  made  for  the  purpose  of 
determining  if  the  thermal  death  point  of  patho- 
genic bacteria,  as  indicated  by  laboratory  tests, 
could  be  safely  relied  upon  under  commercial  con- 
ditions. In  their  experiments  the  investigators  in- 
troduced germs  of  tuberculosis,  diphtheria,  and 
typhoid  fever,  into  milk,  which  was  then  run 

*The  Journal  of  Medical  Research  Vol.  XXVI  NO.  1. 
25 


THE    PASTEURIZATION    OF    MILK 

through  a  commercial  pasteurizer  and  heated  to 
different  temperatures,  and  held  for  varying  lengths 
of  time.  The  results  obtained  indicated  that  when 
an  attempt  was  made  to  heat  this  milk  in  a  com- 
mercial pasteurizer  to  a  temperature  of  140°  F.,  and 
then  hold  it  for  twenty  minutes,  there  was  a  con- 
siderable unavoidable  variation  in  the  actual  tem- 
perature to  which  the  machine  was  capable  of 
heating  the  milk.  This  was  due  to  the  difficulties 
of  both  hand  and  automatic  temperature  control. 
Even  with  the  best  automatic  controller,  it  is 
probable  that  the  real  variation  of  temperature  is 
greater  than  is  indicated  upon  the  record  charts. 
Thermometers  are  not  usually  sufficiently  sensitive 
to  record  rapid  fluctuations  in  temperature.  It  is 
also  true  that  thermometers  indicate  average  tem- 
peratures only,  and  it  is  possible  that  certain  por- 
tions of  the  milk,  the  temperature  of  which  is  con- 
siderably below  this  indicated  average,  pass 
through  the  apparatus. 

In  regard  to  the  time  held  also,  especially  when 
a  continuous  or  flow  type  holding  apparatus  is 
used,  great  uncertainty  exists.  It  is  impossible  to 
be  sure  that  the  time  is  the  same  as  intended.  The 
rate  of  flow  varies,  and  there  is  also  more  or  less 
26 


FROM    THE    PRACTICAL    VIEWPOINT 

mixing  of  the  milk  due  to  various  causes,  which 
will  be  discussed  later. 

Schores  and  Rosenau  found  that  pathogenic  bac-  ^ 
teria  were  not  all  killed  when  the  factors  of  tem- 
perature and  time  were  attempted  which  had  been 
found  effective  in  laboratory  tests.  They  there- 
fore recommended,  in  order  to  provide  a  sufficient 
margin  of  safety,  that  all  milk  he  heated  to  a 
temperature  of  at  least  145°,  and  there  held  for 
no  less  than  twenty-five  minutes.  This  opinion  is 
shared  by  most  persons  who  have  made  a  study 
of  the  subject.  The  New  York  City  Department 
of  Health,  in  1Q14,  so  modified  its  regulations  as 
to  require  that  pasteurized  milk  be  heated  to  from 
142°  to  145°  F.  for  at  least  thirty  minutes. 

While  the  destruction  of  all  pathogenic  bac- 
teria in  milk  is  the  primary  concern  of  health  au- 
thorities, there  are  certain  other  considerations 
which  have  weight  with  them,  and  among  these 
is  the  effect  which  heat  has  upon  the  chemical 
characteristics  of  the  milk.  It  has  been  found  that 
when  milk  is  heated  to  say  160°  F.  or  over,  some 
of  the  constituent  parts  of  the  milk  are  changed  in 
such  a  way  as  to  make  it  somewhat  inferior  as  a 
food,  especially  for  infants.  These  changes  have 

27 


THE    PASTEURIZATION    OF    MILK 

been  somewhat  extensively  studied  by  the  United 
States  Government  experts,  and  it  has  been  found 
that  as  the  temperature  rises  above  160°  F.,  these 
changes  take  place  to  an  increasing  extent,  and  at 
the  boiling  point  quite  extensive  changes  are  ob- 
served. At  this  temperature,  the  milk  sugar  be- 
comes scorched,  the  casein  and  the  albumin  are 
somewhat  hardened,  the  calcium,  magnesium  and 
phosphoric  salts  are  partially  precipitated,  all  of 
which  renders  the  milk  less  easily  digested.  It 
therefore  follows  that  the  lowest  temperature 
which  is  consistent  with  the  destruction  of  the 
pathogenic  bacteria  is  the  most  desirable. 

It  is  also  true  that  milk  which  contains  an  ex- 
cessive number  of  bacteria  carries  with  it,  as  a  re- 
sult of  their  growth,  certain  by-products,  such  as 
acids  and  other  undesirable  substances,  and  may 
also  contain  dangerous  poisons.  Rosenau  states 
that  the  known  poisons  which  are  produced  by  the 
growth  of  bacteria  in  milk  are  very  few,  but  that 
such  poisons  may  possibly  exist  and  produce  harm- 
ful effects  upon  the  persons  using  the  milk.  These 
by-products  of  bacterial  growth  in  milk  are  not 
entirely  destroyed  by  heating,  even  when  the  boil- 
ing temperature  is  attained.  For  this  reason  it  is 
28 


FROM    THE    PRACTICAL    VIEWPOINT 

desirable  that  milk  which  is  to  be  pasteurized  shall, 
before  it  is  heated,  be  as  free  as  possible  from  all 
bacteria.  It  is  this  consideration  which  has  led 
health  authorities  to  insist  that  the  milk  before  pas- 
teurization shall  not  contain  an  excessive  number 
of  bacteria. 

Milk  dealers  know  that  their  customers  com-1' 
monly  judge  of  the  richness  of  the  milk  by  the 
amount  of  cream  which  appears  upon  the  top  of 
the  bottle.  For  this  reason  the  showing  of  a 
"good  cream  line"  is  one  of  the  things  for  which 
the  milk  dealer  strives.  In  some  parts  of  Europe 
the  cream  is  thoroughly  mixed  in  the  milk  by 
homogenizing  it,  so  that  the  cream  will  not  rise, 
but  the  American  housewife  is  not  educated  to  this 
custom,  and  therefore  anything  which  interferes 
with  the  apparent  volume  of  cream  on  the  milk  is 
a  stumbling-block  to  the  milk  dealer.  It  has  been 
found  that  milk  which  is  heated  to  a  temperature 
of  148°  F.  or  over  and  is  held  for  any  consid- 
erable period  of  time,  will  have  its  cream  line  de- 
stroyed, or  at  least  be  made  indistinct.  When 
milk  is  heated  to  a  temperature  lower  than  this 
and  is  held  for  a  great  length  of  time,  the  same 
effect  is  produced.  There  are  other  reasons  which 


THE    PASTEURIZATION    OF    MILK 

interfere  with  the  cream  line  which  will  be  dis- 
cussed later. 

Another  objection  which  customers  urge  against 
pasteurized  milk  is  that  it  has  a  distinctly 
scorched  or  cooked  taste.  This  is  undoubtedly  true 
when  the  milk  is  heated  to  a  high  temperature,  or 
when  an  uneven  temperature  is  maintained.  If  the 
heating  medium  is  kept  at  a  point  greatly  above 
the  temperature  to  which  the  milk  is  to  be  raised, 
the  same  effect  is  produced.  On  account  of  this 
cooked  taste  it  is  evident  that  there  is  a  commer- 
cial objection  to  pasteurization  where  it  is  not 
properly  or  carefully  done. 

Moreover,  when  a  low  temperature  of  heating  is 
used,  the  enzymes  are  not  much  affected,  while 
they  are  destroyed  when  a  high  temperature  is  ap- 
plied. Indeed,  the  Storch  test,  which  is  used  to 
determine  whether  skim  milk  has  been  heated  to 
165°  or  higher  in  compliance  with  the  laws  in  this 
regard,  depends  upon  the  non-action  of  the  en- 
zymes. These  are  destroyed  by  high  heating. 
This  test  is  of  little  or  no  value  in  testing  milk 
pasteurized  at  low  temperature. 

Since  an  even  heating  at  comparatively  low 
temperatures  and  a  holding  for  a  long  time  secures 
30 


FROM    THE    PRACTICAL    VIEWPOINT 

the  desired  result  in  the  destruction  of  bacteria, 
and  at  the  same  time  produces  none  of  the  unde- 
sirable effects  which  follow  when  a  high  tem- 
perature is  employed,  it  is  evident  that  this 
method  of  procedure  is  that  which  is  much  to  be 
preferred. 

To  summarize  the  considerations  which  have x 
just  been  discussed,  it  is  evident  that  the  pastur- 
ized  milk  which  most  nearly  fulfills  the  require- 
ments desired  by  health  authorities,  and  at  the 
same  presents,  from  the  commercial  aspect,  the 
least  objections,  must  conform  to  the  following  de- 
mands : 

First:  Before  pasteurization  it  must  contain  only 
a  small  number  of  bacteria. 

Second:  When  it  is  heated  it  must  be  subjected 
to  a  temperature  which  destroys  all  pathogenic  or 
disease-producing  bacteria,  and  also  a  large  per- 
centage of  bacteria  of  all  other  kinds. 

Third:  Its  constituents  must  be  very  little 
changed  or  altered  by  excessive  heating.  Its  nu- 
tritive value  must  not  be  impaired,  and  its  diges- 
tive enzymes  must  be  uninjured. 

Fourth:  The  taste  of  the  milk  must  not  be  no- 
ticeably changed. 

31 


THE    PASTEURIZATION    OF    MILK 

Fifth:  The  apparent  volume  of  cream  must  not 
be  reduced. 

In  so  far  as  these  factors  represent  results 
which  are  properly  demanded  by  health  authori- 
ties, there  are,  broadly  speaking,  two  general 
methods  by  which  they  can  be  controlled  when 
their  control  depends  upon  the  powers  exercised 
by  the  municipality  or  the  state.  One  of  these 
may  be  called  the  laboratory  method)  and  the 
other  the  inspectional  method.  When  the  labora- 
tory method  is  employed  it  is  necessary  that  cer- 
tain definite  chemical  and  bacteriological  standards 
be  adopted,  which  apply  to  pasteurized  milk  or  to 
milk  which  is  to  be  pasteurized.  Some  of  these 
standards  may  depend  upon  color  reactions.  Such 
standards  being  in  force,  the  effectiveness  of  con- 
trol depends  upon  the  frequent  examination  of  sam- 
ples of  milk  taken  before  and  during  the  process 
of  pasteurization  and  as  it  is  offered  for  sale.  If 
the  tests  show  that  the  milk  conforms  to  the  legal 
standards,  it  may  be  judged,  with  a  fair  degree  of 
confidence,  that  the  apparatus  employed  in  pas- 
teurizing and  handling  the  milk  is  properly  in- 
stalled and  operated. 

When  the  inspectional  method  of  control  is  em- 

S2 


FROM    THE    PRACTICAL    VIEWPOINT 

ployed,  it  is  necessary  that  certain  definite  regula- 
tions be  adopted  which  shall  specify  on  broad  lines 
the  form  of  apparatus  which  must  be  used,  how 
it  shall  be  installed  and  how  it  shall  be  operated. 
The  construction  and  arrangement  of  the  build- 
ings and  of  the  various  rooms  may  be  specified,  it 
having  been  determined  by  previous  experience 
that  such  and  such  apparatus  and  surroundings 
operated  and  handled  in  such  and  such  a  way  will 
produce  milk  which  will  be  of  the  character  de- 
sired. With  these  regulations  in  force,  it  is  pos- 
sible, by  frequent  and  careful  inspections  made  of 
pasteurizing  plants,  to  determine  whether  or  not 
the  legal  regulations  are  being  faithfully  observed. 
If  it  is  found  that  they  are  complied  with,  then  it 
is  logical  and  safe  to  conclude  that  the  milk  pro- 
duced is  of  suitable  character,  and  will  satisfac- 
torily respond  to  all  suitable  chemical  and  bac- 
teriological tests  which  may  be  applied. 

As  a  matter  of  fact,  neither  method  of  control 
is  used  by  authorities  to  the  exclusion  of  the  other, 
but  a  combination  of  the  two  methods  is  found  to 
be  the  most  satisfactory.  In  some  cities  the  em- 
phasis is  placed  upon  laboratory  tests,  with  in- 
spections made  to  confirm  the  results.  In  other 

S3 


THE    PASTEURIZATION    OF    MILK 

places,  the  emphasis  is  upon  physical  regulations 
and  inspections,  with  occasional  laboratory  tests  to 
confirm  the  conclusions  reached  and  to  aid  in  the 
discovery  of  obscure  defects  which  may  escape  ob- 
servation during  the  usual  inspections.  No  advice 
can  be  given  as  to  which  method  is  most  desirable 
without  first  knowing  local  conditions,  taking  into 
account  the  extent  of  the  milk  industry,  the  avail- 
able factors  of  men,  money  and  laboratory  equip- 
ment, etc.  Each  community  presents  its  individ- 
ual problem. 

Health  authorities  are  often  requested  by  milk 
dealers  to  give  advice  as  to  the  form  of  pasteurizing 
apparatus  which  will  perform  the  best  work,  or 
they  are  asked  what  kind  of  machine  the  authorities 
recommend.  It  is  manifestly  improper  for  health 
authorities  to  recommend  specifically  any  one  or 
more  forms  of  apparatus  as  the  best.  If  they  did, 
they  would  lay  themselves  open  to  the  charge  of 
unfair  favoritism,  and  to  the  suspicion  that  im- 
proper influence  determined  their  judgment.  It 
is  only  proper  that  they  should  state  that  in  their 
experience  certain  forms  of  apparatus,  operated 
in  certain  ways,  have  performed  certain  things  in 
actual  practice  which  are  or  are  not  satisfactory 

34 


FROM    THE    PRACTICAL    VIEWPOINT 

to  those  who  are  responsible  for  this  condition  of 
the  milk.  Indeed,  when  advice  is  asked  as  to  the 
form  of  apparatus  most  desirable  to  be  installed 
at  a  given  point,  it  is  impossible  to  solve  such  a 
problem  without  possessing  complete  knowledge  of 
the  conditions  which  surround  each  plant  where  it 
is  desired  to  install  a  pasteurizer.  Each  plant  ^ 
presents  an  individual  problem  of  its  own,  which 
must  be  carefully  studied,  having  clearly  in  mind 
all  the  facts  which  specially  relate  to  the  plant  in 
question.  It  is  impossible  to  place  too  much  em- 
phasis upon  this  point,  since  time  and  money  and 
the  securing  of  expert  advice  before  the  construc- 
tion and  equipment  of  a  plant  will  frequently  bring 
continuous  dividends  in  convenience,  in  the  saving 
of  time,  in  preventing  needless  waste  of  money, 
and  in  the  general  satisfaction  which  accompanies 
the  successful  operation  of  an  efficient  plant. 

Among  the  factors  to  be  considered,  the  con-  ~ 
struction  and  physical  characteristics  of  the  build- 
ing where  the  plant  is  to  be  located  is  of  impor- 
tance in  determining  the  selection  of  the  appara- 
tus to  be  used.  Again,  the  distance  of  the  plant 
from  the  point  where  the  milk  is  to  be  distributed 
and  consumed  should  be  considered.  If  located 

35 


THE    PASTEURIZATION    OF    MILK 

in  the  country  at  a  distance  from  the  city,  the  ele- 
ment of  time  available  after  the  milk  is  delivered 
by  the  dairyman  is  also  an  important  item.  The 
amount  of  milk  to  be  pasturized  daily,  and  the 
use  which  is  to  be  made  of  the  finished  product 
have  a  bearing  upon  the  final  decision.  With 
many  dealers  the  question  of  expense  may  be  of 
first  importance,  but  it  must  be  borne  in  mind 
that  cheap  installation  does  not  always  mean  econ- 
omy. The  question  of  expense  involves  both  the 
initial  cost  of  installation  and  the  outlay  for  oper- 
ation and  upkeep.  Where  the  matter  of  furnish- 
ing sufficient  steam  is  a  point  for  serious  con- 
sideration, or  where  water  expense  affects  the  final 
cost,  it  is  desirable  to  use  those  forms  of  appara- 
tus which  consume  the  fewest  heat  units  and  which 
use  the  least  amount  of  water.  There  are  also 
other  considerations  which  will  be  discussed  later, 
and  it  will  be  found  that  at  many  plants  unique 
conditions  exist  which  must  be  carefully  studied. 

On  broad  lines,  however,  it  may  be  stated  that 
a  pasteurizing  plant,  in  order  to  be  as  nearly  as 
possible  ideal  in  regard  to  its  construction,  and 
which  will  at  the  same  time  be  capable  of  produc- 
ing a  milk  which  will  be  satisfactory  from  the 


FROM    THE    PRACTICAL    VIEWPOINT 

standpoint  of  safety  and  wholesomeness,  and  will 
also  satisfy  commercial  demands,  should  combine 
the  following  features: 

1.  The  Building. — The  building  where  the  plant  V 
is  located  should  contain  ample  space  and  should, 

if  possible,  be  so  arranged  that  the  milk  will  flow 
by  gravity  from  the  point  of  receipt,  or  where 
cans  are  emptied  to  the  point  where  it  is  taken  out 
for  delivery  or  transportation. 

2.  Separate  Rooms. — The  various  stages  in  the  v 
process   of  treating  the   milk,   such   as   receiving, 
pasteurizing,    cooling,    filling    containers,    storage 
and  of  washing  the  containers,  should  be  carried 
on  in  separate,  clean,  well-lighted  and  ventilated 
rooms  or  compartments. 

3.  Protection     from     Contamination.  —  At     all 
points   during  the  process   of  handling,  the   milk 
should   be   protected    against   contamination    from 
contact  with  unclean  apparatus,  and  from  infec- 
tion by  means  of  dust-laden  air.     This  protection 
is  especially  necessary  after  the  holding  process 
is  completed.     Any  infection  occurring  after  this 
time  is  not  corrected  by  heating,  and  may  there- 
fore be  a  source  of  danger. 

4.  Constant    Temperature. — The  heating   appa- 

37 


THE    PASTEURIZATION    OF    MILK 

ratus,  whatever  its  form,  should  be  capable  of 
heating  every  particle  of  milk  to  a  temperature 
which  will  never  be  below  that  to  which  it  is  the 
intention  that  it  shall  be  heated.  For  instance, 
if  it  is  intended  to  heat  to  140°,  the  temperature 
should  not  fluctuate  between  135°  and  145°,  but 
should  remain  constantly  at  140°  or  over. 

5.  Method  of  Heating. — The  heating  should  be 
accomplished   by   an   apparatus   which   allows   the 
milk  to  flow  over  a  clean  metal  surface,  which  is 
kept  hot  by  means  of  heated  water,  and  not  by 
direct  steam  contact.     This  hot  water  should  never 
have  a  temperature  more  than  10°  or  15°  higher 
than  that  to  which  it  is  desired  to  heat  the  milk. 

6.  Holding   Apparatus. — The    holding    appara- 
tus, whether  the  absolute  or  the  continuous   flow 
type  process  is  employed,  should  be  so  constructed 
and    operated    that    it   will    definitely    insure    the 
holding  of  every  particle  of  the  milk  without  fail 
for  the  desired  length  of  time. 

7.  Recorders. — The    temperature    to    which    the 
milk  is  heated  must  be  automatically  recorded,  and 
should  be   automatically   controlled.      It   is   desir- 
able that   a  temperature   recording  device  be   in- 
stalled   at   the   point   where   the    milk   leaves   the 

38 


FROM    THE    PRACTICAL    VIEWPOINT 

heating  apparatus  and  that  another  recorder  be 
attached  to  the  outlet  pipe  from  the  holder.  This 
latter  recorder  indicates  whether  or  not  any  great 
amount  of  heat  has  been  lost  during  the  holding 
process,  and  also  shows  whether  the  apparatus  is 
thoroughly  heated  before  the  milk  is  admitted.  If 
not  so  heated,  the  first  milk  leaving  the  holder 
will  have  been  somewhat  cooled,  and  the  recorder 
will  indicate  this.  After  the  apparatus  has  been 
in  operation  for  a  considerable  time,  it  will  then 
acquire  the  temperature  of  the  milk,  which  will 
then  pass  out  with  the  temperature  but  little  di- 
minished. These  observations  do  not  apply  to  a 
tank  or  batch  pasteurizer.  In  this  case  a  single 
recorder  attached  to  the  tank  itself  shows  all  that 
is  necessary.  It  also  indicates  the  time  for  which 
the  milk  is  held  at  the  required  temperature. 

8.  Pumps  and  Pipings. — The  amount  of  milk 
piping  in  use  should  be  reduced  to  the  minimum 
requirements.  All  piping  which  is  used  should 
be  of  sanitary  construction,  with  the  joints  and 
turns  so  arranged  that  they  can  be  easily  taken 
apart  for  cleaning.  As  before  stated,  the  appara- 
tus should  be  so  arranged  that  the  milk  will  flow 
by  gravity  from  point  to  point  in  the  process  of 

39 


THE    PASTEURIZATION    OF    MILK 

treatment.  If,  however,  it  is  necessary  to  use  milk 
pumps,  they  should  be  of  absolutely  sanitary  con- 
struction. The  use  of  pumps  for  moving  the  raw 
milk  is  less  objectionable  than  is  their  use  for  mov- 
ing pasteurized  milk.  Not  only  is  the  danger  of 
infection  by  means  of  unclean  pumps  very  serious, 
but  if  the  milk  is  pumped  while  hot,  the  cream  is 
so  disturbed  that  it  does  not  rise  as  readily  as  is 
desirable. 

9.  Rubber  Fittings   and   Gaskets. — The   use   of 
rubber   fittings,   of   gaskets   and   of   stuffing-boxes 
should  be  avoided. 

10.  Cooling. — The  milk  should  be  immediately 
and   rapidly   cooled,   to   a   temperature   as   nearly 
40°  F.  as  possible.     This  cooling  should  be  accom- 
plished within  thirty  minutes  after  the  heating  and 
holding  .process  is  completed.     Except  where  cool- 
ing is  carried  on  in  the  tanks  where  it  is  heated, 
the  cooling  can  be  completed  in  much  less  than 
thirty  minutes.     The  milk  should  be,  of  course, 
kept  cold  until  delivered  to  the  consumer. 

11.  Cleaning     of     Containers. — All     containers, 
including  cans,  covers  and  bottles,  should  be  com- 
pletely and  if  possible  automatically  washed  and 
sterilized.     They  should  then  be  thoroughly  dried 

40 


FROM    THE    PRACTICAL    VIEWPOINT 

and  should  be  stored  in  clean,  cold  rooms,  and  there 
kept  inverted  or  carefully  covered  until  filled. 

12.  Cleaning     of     Apparatus. — All     apparatus 
used  in  handling  milk  should  be  carefully  washed 
and   sterilized  after  its   use,  and  all  of  it  which 
comes    in    contact    with    the    pasteurized    product 
should  be  again  sterilized  before  its  use  each  day.    v 

13.  Healthy  Employees. — All  persons  employed 
in  handling  the  milk  should  be  known  to  be  healthy 
and    free    from    any    infectious    disease.       They 
should  be  clean  in  their  person  and  habits,  and 
should  wear  special  clean  clothing,  preferably  of 
white  material,  while  handling  milk. 

14.  Bottle    Capping. — The    milk    bottles,    after 
filling,  should  be  capped  by  clean  machinery,  thus 
avoiding  as   far  as  possible  any  personal  contact 
with  the  milk  after  it  is  pasteurized. 

It  is  needless  to  say  that  all  the  ordinary  precau- 
tions regarding  the  sanitary  construction  of  build- 
ings where  food  is  handled  should  be  observed, 
and  the  close  proximity  of  stables  or  other  con- 
taminating influences  should  be  avoided. 

There  are,  of  course,  many  other  points  of  de- 
tail in  the  construction  and  operation  of  pasteur- 
izing plants  which  will  repay  careful  attention. 

41 


THE    PASTEURIZATION    OF    MILK 

These  will  be  touched  upon  in  the  following  pages. 
On  broad  lines,  however,  it  may  be  said  that  if  the 
foregoing  conditions  ar/e  carefully  fulfilled,  then 
it  will  be  possible  to  obtain  a  good  safe  milk  which 
the  public  may  consume  with  a  feeling  of  security, 
and  which  should  satisfy  all  requirements  of  health 
authorities. 

It  is  not  proper,  of  course,  to  recommend  any 
specific  type  or  form  of  apparatus  to  be  used  in 
pasteurizing  milk.  It  is  proposed,  however,  to  de- 
scribe in  the  following  pages  and  to  show  by  dia- 
gram or  illustration  the  construction  and  operation 
of  different  makes  of  apparatus,  and  to  call  atten- 
tion to  those  points  in  each  which  experience  has 
taught  are  of  advantage  or  disadvantage. 


CHAPTER    II 

HEATERS 

In  1909  the  New  York  City  Department  of 
Health  first  adopted  the  rule  which  required  that 
milk  could  not  be  considered  as  pasteurized  un- 
less it  had  been  heated  to  a  definite  temperature 
and  held  at  this  temperature  for  a  certain  definite 
length  of  time.  New  York  was  the  pioneer  in 
requirements  of  this  sort. 

At  this  time  various  forms  of  milk  heaters  were 
on  the  market,  but  no  device  was  available  for 
holding  the  heated  milk.  All  heaters  employed 
a  process  which  is  known  as  the  continuous  or  flash 
process  of  heating.  By  this  process  the  milk 
flowed  or  was  forced  in  a  continuous  stream 
through  the  apparatus,  where  it  was  subjected  to 
an  amount  of  heat  which  was  not  very  definite,  and 
which  was  controlled  by  the  hand  of  the  operator. 
The  milk  was  then  immediately  cooled. 

Most   of   the    forms    of   apparatus    which   were 

then  on  the  market  are  still  in  use,  and  certain  new 

forms  of  heaters  have  been  invented.     Certain  new 

types   of  apparatus  were   devised   as   adjuncts   of 

43 


THE    PASTEURIZATION    OF    MILK 

the  heaters,  into  which  the  milk  was  allowed  to 
flow  from  the  heaters  and  in  which  the  hot  milk 
was  held  for  the  time  required  by  the  regulations. 

As  before  stated,  the  forms  of  heaters  in  use 
in  1909  are  still  employed,  with  certain  new  forms 
made  by  many  different  manufacturers.  They  are 
all  comprised  under  some  one  of  five  typical  forms, 
as  follows: 

First  Type. — The  so-called  Danish  heater  is 
sold  by  various  firms.  It  is  shown  in  the  accom- 
panying illustrations  (Figs.  1  and  2).  This  is 
the  oldest  form  of  heater  in  use  in  this  country. 
In  this  form  a  large  central  cylinder  is  provided 
with  a  double  cover  or  jacket.  The  space  between 
the  inner  and  outer  shell  is  filled  with  water,  into 
which  steam  is  introduced.  By  means  of  a 
suitable  device  the  steam  is  distributed  through  the 
water  at  various  points. 

In  operation,  the  milk  is  allowed  to  flow  or  is 
pumped  into  the  inner  compartment  or  cylinder, 
and  by  means  of  rapidly  revolving  paddles  it  is 
thrown  by  centrifugal  force  against  the  inner  sur- 
face of  the  cylinder.  This  surface  is  kept  hot  by 
means  of  the  hot  water  and  steam  in  the  outer 
shell.  The  milk  enters  at  the  bottom  of  the  cylin- 

44 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  1 


FIG.  2 


der,  and  since  the  outlet  pipe  at  the  top  is  placed 
at  a  tangent  to  the  cylinder,  the  rotating  paddles 
tend  to  throw  the  milk  out  of  the  pipe.  The  ma- 
chine therefore  acts  somewhat  as  a  pump,  and 
when  the  whole  machine  is  set  at  an  angle  from 
the  perpendicular,  this  tendency  to  throw  the  milk 
is  enhanced  and  the  milk  can  be  lifted  about  fifteen 
feet.  This  fact  is  one  of  the  advantages  of  the 
machine.  Another  advantage  is  that  it  is  com- 
paratively inexpensive,  since  it  is  rather  small.  Its 
45 


THE    PASTEURIZATION    OF    MILK 

size  also  tends  toward  the  ease  of  cleaning,  there 
being  no  great  amount  of  surface  with  which  the 
milk  comes  in  contact. 

This  very  fact,  however,  that  the  heating  sur- 
face is  small  in  area,  is  also  a  disadvantage,  for 
it  renders  it  necessary  to  raise  the  temperature  of 
the  heating  medium  to  a  point  so  high  that  it  is 
frequently  very  much  in  excess  of  that  to  which 
it  is  the  desire  to  heat  the  milk.  The  result  is 
that  certain  portions  of  the  milk  reach  a  tempera- 
ture so  high  that  a  distinctly  scorched  taste  is  im- 
parted to  it.  This  taste  persists  in  the  entire 
body  of  the  treated  milk,  even  though  the  average 
temperature  of  the  milk  leaving  the  apparatus  is 
below  145°.  This  is  especially  noticeable  if  the 
flow  of  milk  into  the  apparatus  fluctuates.  It  can 
be  readily  seen  that  with  a  very  hot  heating  sur- 
face, and  at  the  same  time  a  small  amount  of  milk 
passing  through  the  machine  due  to  a  sudden  stop- 
page of  flow,  this  milk  would  attain  a  high  tem- 
perature. 

This  superheating  of  even  a  portion  of  the  milk 
tends  to  cause  an  interference  with  the  normal 
rising  of  the  cream,  after  the  milk  is  placed  in 
containers.  The  vigorous  agitation  of  the  hot  milk 

46 


FROM    THE    PRACTICAL   VIEWPOINT 

by  means  of  the  paddles  also  has  a  tendency  to 
break  up  the  fat  globules  into  smallei  particles, 
which  do  not  so  readily  rise  to  the  surface. 

It  is  difficult  to  maintain  a  uniform  temperature 
with  this  type  of  machine,  since  the  amount  of 
heating  fluid  is  comparatively  small,  and  when 
there  is  either  a  fluctuating  flow  of  milk  or  a  vary- 
ing milk  temperature,  there  is  no  automatic  con- 
troller which  can  be  made  to  respond  to  sudden 
changes  in  temperature  quickly  enough  to  check 
or  increase  the  flow  of  steam  into  the  heating 
chamber. 

As  a  general  proposition,  also,  the  introduction 
of  steam  directly  into  a  heating  chamber  is  to  be 
avoided,  since  there  is  always  the  possibility  that 
certain  portions  of  the  steam  will  strike  the  heat- 
ing surface  before  becoming  condensed,  and  will 
therefore  heat  these  portions  to  an  abnormally 
high  point. 

Second  Type. — There  are  several  heating  de- 
vices made  by  different  firms,  and  having  certain 
variations  in  the  details  of  their  construction, 
which  embody  the  same  general  principles.  These 
are  illustrated  in  Figs.  3,  4,  5.  In  all  of  these 
the  milk  flows  between  two  or  more  upright,  heated 

47 


THE    PASTEURIZATION    OF    MILK 


FIG.  3 

1 — Discharge  of  warmed  milk  to  gathering  tank. 

2 — Return  of  warmed  milk  to  interior  of  heater. 

3 — Discharge  of  heated  milk  to  holder. 

4 — Hot  water  intake. 

5 — Return  of  held  milk  to  regenerator. 

6 — Cold  milk  entering  hea.ter. 

7 — Discharge  of  partly  cooled  miik  tp  cooler. 

48 


FROM    THE    PRACTICAL    VIEWPOINT 


THE    PASTEURIZATION    OF    MILK 


FIG.  4-B 

cylindrical  surfaces.  The  heating  surfaces  are 
kept  at  the  desired  temperature  by  means  of  hot 
water,  which  in  turn  is  heated  either  by  the  intro- 
duction of  steam  into  the  water  chamber  directly, 
or  by  heating  the  water  in  tanks  outside  the  milk 
50 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  5 

1 — Interior  water  tank. 
2 — Exterior  water  tank. 
3 — Space  between  water  tanks,  through  which  milk  is  forced  upward. 

51 


THE    PASTEURIZATION    OF    MILK 

apparatus.  From  these  tanks  it  is  pumped  into 
the  heating  chambers.  Where  steam  enters  di- 
rectly into  the  milk  apparatus  the  same  objections 
obtain  which  were  noticed  in  the  description  of  the 
Danish  type  of  heater.  Superheating  of  the  milk 
in  whole  or  in  part,  an  objectionable  cooked  taste, 
interference  with  the  cream  line,  etc.,  are  likely  to 
follow.  Where  an  outside  heating  tank  is  employed, 
it  is  comparatively  easy  to  keep  the  water  at  a 
nearly  uniform  temperture  by  means  of  a  thermo- 
stat, which  controls  the  introduction  of  steam. 
With  this  heated  water  being  pumped  to  the  milk- 
heating  apparatus,  it  is  certain  that  the  milk  can 
never  get  above  the  temperature  to  which  the  water 
is  heated,  and  if  this  water  is  not  more  than  10°  or 
15°  hotter  than  the  temperature  at  which  it  is  the 
intention  to  heat  the  milk,  no  serious  superheating 
can  result.  This  point  will  be  more  fully  de- 
scribed later. 

In  all  heaters  of  this  type  some  method  is  em- 
ployed to  keep  the  milk  in  constant  motion  as  it 
flows  upward  between  the  heating  surfaces,  thus 
insuring  that  all  portions  of  milk  come  in  contact 
with  their  surfaces.  In  the  machine  illustrated  in 
Fig.  3  this  agitation  is  accomplished  by  means  of 
52 


FROM    THE    PRACTICAL    VIEWPOINT 

a  revolving  arm,  which  extends  into  the  milk  space 
between  the  inner  and  the  outer  water  chambers. 
In  Fig.  5,  the  inner  cylinder  revolves  and  the  nar- 
row corrugation  which  extends  in  a  spiral  form 
around  the  cylinder  forces  the  milk  upward.  The 
shaft  which  operates  these  stirring  devices  in  some 
instances  comes  in  contact  with  the  milk,  and  in 
order  to  prevent  leakage,  it  is  necessary  to  pro- 
vide some  sort  of  packing  or  stuffing  box.  This 
is  a  disadvantage,  since  nearly  all  packing  is  some- 
what porous,  and  it  is  difficult  to  keep  clean. 

Heaters  constructed  in  this  general  form  have 
been  found  to  be  effective  in  operation,  and  good 
results  have  been  obtained  by  their  use.  They 
have  been  found  to  be  durable  as  well.  Some  in- 
dividual machines  have  been  in  use  for  ten  years, 
which  indicates  the  carefulness  with  which  they 
have  been  constructed.  Those  forms  of_heaters 
are  the  most  satisfactory  in  which  the  greatest 
amount  of  heating  surface  is  available,  and  where 
the  amount  of  hot  water  which  circulates  through 
the  apparatus  is  relatively  large.  These  conditions 
render  it  possible  to  use  water  which  has  a  com- 
paratively low  temperature. 

Some  of  these  heaters  employ  what  is  known 
53 


THE    PASTEURIZATION    OF    MILK 

as  the  "regenerative  principle."  This  means  that 
the  hot  milk  which  flows  from  the  machine  is  em- 
ployed for  warming  the  cold  milk  which  flows  into 
the  apparatus  to  be  heated.  When  this  regenera- 
tive principle  is  used,  a  considerable  economic  sav- 
ing of  heat  units  is  secured.  This  saving  means 
that  less  steam  is  required  for  heating,  and  also  that 
less  ice  is  necessary  for  cooling.  In  the  type  illus- 
trated in  Fig.  4  the  milk  flowing  from  the  holder 
is  conveyed  to  a  holding  apparatus,  and  after  be- 
ing held  is  returned  to  the  heater,  where  it  flows 
through  another  compartment  and  helps  to  heat 
the  inflowing  cold  milk. 

At  least  one  form  of  regenerative  heater  (Fig. 
6)  is  so  constructed  that  this  intermediate  holding 
process  cannot  be  used.  In  sections  of  the  country, 
therefore,  where  city  regulations  require  that  the 
heated  milk  be  held  for  a  definite  period,  this  form 
of  heater  cannot  be  used.  As  a  so-called  "flash" 
pasteurizer,  this  machine  has  given  good  results. 

In  Fig.  4-B  is  shown  a  form  of  heater  in  which 
the  hot  water  is  contained  on  the  inside  of  the  lower 
cone.  The  milk  flows  from  the  top  over  the  heated 
cone.  Revolving  arms  to  which  is  attached  a  heavy 
cord,  keep  the  cone  surface  wiped,  and  prevent 
54 


FROM    THE    PRACTICAL    VIEWPOINT 


55 


THE    PASTEURIZATION    OF    MILK 

the  milk  from  sticking  to  the  heated  surface. 
There  is  difficulty  in  keeping  the  cord  clean  and 
sanitary. 

Third  Type. — The  tubular  type  of  heater  is 
manufactured  and  sold  by  several  concerns.  In 
all  of  these  forms,  the  milk  flows  through  tubes, 
which  are  themselves  surrounded  by  some  heating 
medium,  usually  hot  water.  In  the  form  shown 
in  Fig.  7  the  milk  tube  is  enclosed  by  a  larger 
tube,  through  which  hot  water  flows  in  a  direction 
opposite  to  the  milk  flow.  In  forms  which  are 
illustrated  by  Figs.  8,  9  and  10  the  heating  water 
is  contained  in  boiler-like  structures,  through 
which  the  tubes  extend.  Care  must  be  exercised 
in  order  to  make  sure  that  there  can  be  no  leak- 
age between  the  milk  tubes  and  the  water  con- 
tainers. In  Fig.  7  the  couplings  between  the  vari- 
ous milk  pipes  in  the  series  are  outside  of  and 
beyond  the  water  couplings,  so  that  no  mixing  of 
the  milk  and  water  can  occur  unless  there  is  a 
broken  milk  pipe.  In  Figs.  8,  9  and  10  the  milk 
tubes  are  either  braized  or  expanded  into  the  heads, 
and  the  danger  of  leakage  is  slight.  Of  course, 
when  heat  is  applied  to  these  tubes,  the  tendency 
is  for  them  to  expand  and  so  become  more  tightly 
56 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  7 


fixed  in  the  heads.  Sudden  and  wide  variations  of 
temperature  would  tend  to  loosen  the  joints.  The 
flowage  of  the  water  in  a  direction  opposite  to  milk 
flow  brings  the  hottest  water  against  those  milk 
tubes  where  the  hottest  milk  is  found.  As  the 

57 


THE    PASTEURIZATION    OF    MILK 


•;==== 


FIG.  8 


water  flows  along  the  tubes  it  becomes  gradually 
cooled  by  the  cooler  milk,  so  that  it  emerges  at  a 
low  temperature.  Thus  the  milk  is  heated  grad- 
ually, and  no  sudden  raising  of  the  temperature 
occurs.  This  renders  the  control  of  the  tempera- 
ture an  easy  matter,  since  sudden  fluctuation  in 
temperature  cannot  readily  occur.  There  is  also 
58 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  9 

an  economical  use  of  the  heat,  and  little  of  it  is 
wasted. 

In  Fig.  11  a  form  of  heater  is  illustrated  in 
which  the  milk  flows  through  a  group  of  small 
tubes,  which  are  themselves  enclosed  in  a  large 

59 


THE    PASTEURIZATION    OF    MILK 


60 


FROM    THE    PRACTICAL    VIEWPOINT 


THE    PASTEURIZATION    OF    MILK 

tube.  The  larger  tube  contains  the  water  which 
surrounds  the  small  tubes  which  contain  the  milk. 
When  the  regenerative  principle  referred  to  is  em- 
ployed, in  this  type  of  heater  the  hot  milk  return- 
ing from  the  holding  tanks  is  allowed  to  flow 
through  the  larger  tube,  and  thus  assist  in  heating 
the  cold  inflowing  milk. 

Tubular  heaters  are  doing  very  satisfactory 
work.  Those  machines  are  in  some  respects  the 
most  efficient  in  which  the  flow  of  milk  is  slow 
enough  or  which  have  a  sufficient  heating  surface 
to  insure  that  all  portions  of  the  milk  will  reach 
the  maximum  temperature.  It  has  been  found 
from  experience  that  when  milk  flows  through 
tubes  which  are  of  comparatively  large  diameter, 
there  is  a  tendency  for  that  portion  of  the  milk 
which  is  in  the  center  of  the  tube  to  flow  faster 
than  that  which  is  close  to  the  inner  surface  of 
the  tube.  This  is  due  to  the  greater  friction  at 
the  point  of  contact.  It  can  be  readily  seen  that 
there  will  therefore  be  a  tendency  for  the  milk 
which  flows  more  slowly  close  to  the  heated  surface 
of  the  tube  to  become  heated  to  a  considerably 
higher  point  than  that  near  the  center.  When 
the  water  entering  the  final  tube  of  the  heater  is 

62 


FROM    THE    PRACTICAL    VIEWPOINT 

high  in  temperature,  there  is  a  certain  amount  of 
danger  of  cooking  or  scorching  the  milk,  and  pos- 
sibly of  breaking  up  the  fat  globules.  It  is  also 
true  that  if  a  coating  of  cooked  milk  forms  on  the 
inner  surface  of  the  tube,  it  acts  as  an  insulating 
material  and  therefore  a  constantly  increasing  tem- 
perature must  be  applied  to  the  water.  The  return 
of  the  milk  from  one  tube  to  another  in  the  series 
tends  to  mix  the  milk  and  so  break  up  the  more 
rapid  flowing  core.  This  breaking  up  process, 
however,  may  have  a  detrimental  effect  upon  the 
fat  content  and  may  render  the  cream  less  likely 
to  rise.  In  one  or  two  instances  known  to  the 
writer  it  was  found  that  when  the  milk  left  the 
apparatus  at  a  temperature  of  only  140°  the  cream 
line  was  considerably  interfered  with. 

The  types  shown  in  Figs.  7,  10  and  11  have  this 
advantage,  namely,  that  since  they  can  be  obtained 
in  sections,  the  pasteurizing  plant  can  be  expanded 
by  the  installation  of  additional  sections  as  the 
growth  of  the  business  demands.  Since  a  cooling 
apparatus  of  exactly  similar  form  is  provided  it  is 
possible  to  extend  the  cooling  facilities  in  the  same 
way.  By  a  proper  interchange  of  the  water  used 
in  both  the  heater  and  cooler,  the  regenerative 
63 


THE    PASTEURIZATION    OF    MILK 

principle  is  made  use  of,  and  the  cool  water  leav- 
ing the  heater  is  carried  over  to  the  cooler,  so  that 
it  helps  to  cool  the  hot  milk  flowing  into  it. 

In  choosing  a  machine  of  this  type,  care  should 
be  exercised  in  securing  one  which  may  be  easily 
cleaned,  especially  at  the  turns  and  joints.  All 
these  should  be  smooth  and  readily  accessible. 

It  should  be  borne  in  mind  that  while  a  large 
heating  area  with  many  pipes  is  an  advantage  in 
securing  an  even  heating  with  a  low  water  tem- 
perature, the  difficulties  of  cleaning  are  also  in- 
creased. 

It  is  also  readily  seen  that  when  powerful  pumps 
force  the  hot  water  rapidly  through  the  heating 
pipes,  a  relatively  lower  heating  temperature  may 
be  employed. 

An  objection  to  the  tubular  form  of  heater  lies 
in  the  fact  that  the  tubes  in  this  system  are  nearly 
'horizontal  and  parallel.  There  is  thus  but  little 
inclination  or  pitch  to  the  tubes,  and  the  milk  flows 
from  them  rather  slowly  when  they  are  emptied  at 
the  close  of  operations  for  the  day.  This  objec- 
tion has  been  overcome  in  some  of  the  more  re- 
cently manufactured  machines,  by  putting  the 
pipes  at  an  incline  and  not  parallel  to  each  other. 
64 


FROM    THE    PRACTICAL    VIEWPOINT 

Thus  the  milk  can  be  more  readily  drained  from 
the  apparatus  when  it  is  being  emptied. 

One  striking  advantage  of  the  tubular  type  of 
apparatus  is  found  in  the  fact  that  it  may  be  very 
thoroughly  sterilized.  Steam  can  be  admitted  into 
all  the  parts  where  the  milk  will  enter,  and  the 
steam  may  be  under  pressure  if  so  desired. 

It  is  important  that  a  machine  of  this  type  be 
so  constructed  that  no  milk  will  leak  from  one 
section  of  tubing  into  another  section,  but  that  it 
all  follows  the  course  which  it  is  intended  that  it 
shall  follow.  In  the  forms  shown  in  Figs.  8f  9 
and  10,  the  doors  at  the  ends  which  cover  the  ends 
of  the  milk  tubes  are  provided  with  gaskets  to 
prevent  this  leakage. 

It  is  well  to  note  whether  or  not  these  gaskets 
are  tight.  In  one  or  two  forms,  the  gaskets  con- 
sist of  sheets  of  metal  which  are  backed  by  felt 
or  rubber  in  such  a  way  that  the  metal  readily 
conforms  to  the  projections  of  the  tubes,  thus  mak- 
ing a  closely  fitting  cover.  The  metal  sheet  can, 
of  course,  be  readily  cleaned. 

Fourth  Type. — The  tank,  or  so-called  batch  sys- 
tem of  heating  milk,  is  quite  largely  employed. 
Heating  tanks  for  this  purpose  are  now  manu: 

65 


THE    PASTEURIZATION    OF    MILK 


66 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  13 


factured  by  many  concerns  which  handle  pasteur- 
izing apparatus.  These  batch  pasteurizers  consist, 
as  shown  in  Figs.  12,  13,  14,  H-B,  1,5,  16,  of  hori- 
zontal tanks,  constructed  sometimes  singly  and 
sometimes  made  with  two  compartments  in  the  same 
apparatus.  In  Fig.  16  we  see  a  tank  which  is  in  the 
form  of  an  upright  cylinder.  These  tanks  are  in 
some  cases  surrounded  by  an  insulating  jacket. 
In  others  there  is  an  open  space  between  the  inner 
and  outer  shell,  through  which  hot  water  is  made 

67 


THE    PASTEURIZATION    OF    MILK 


68 


FROM    THE    PRACTICAL    VIEWPOINT 


THE    PASTEURIZATION    OF    MILK 

to  circulate,  usually  by  means  of  a  pump.  These 
tanks  have,  extending  through  them  in  a  horizon- 
tal direction,  some  form  of  agitator.  This  may  be 
a  tubular  coil,  as  in  Figs.  12,  13  and  14-B,  or  stir- 
ring paddles,  as  in  Fig.  15,  or  it  may  be  coil  sus- 
pended from  above,  as  in  Fig.  16.  Some  of  the 
older  forms  have,  instead  of  a  coil  of  pipe,  a  series 
of  hollow  screw-shaped  discs.  In  some,  as  in  Fig. 
14,  there  is  a  tubular  structure  which  is  suspended 
from  the  top  of  the  tank  and  which  swings  back 
and  forth  by  means  of  a  mechanical  arrangement. 
In  operation,  these  tanks  being  filled  with  milk, 
hot  water  is  forced  through  the  tubes  or  discs 
above  referred  to.  These  coils  rotate,  keep  the 
milk  mixed  and,  at  the  same  time,  heat  it  and  thus 
raise  it  to  the  desired  temperature.  The  circulation 
of  water  is  maintained  in  some  machines  by  means 
of  pumps,  the  steam  for  heating  being  admitted 
into  the  return  water  shortly  before  it  is  again 
forced  through  the  coil. 

In  other  machines,  as  in  Fig.  12,  the  admission 
of  air  into  the  coil  creates  a  suction  which  forces 
the  water  through  without  the  use  of  pumps.  In 
the  form  shown  in  Fig.  15,  the  heating  is  accom- 
plished in  a  rather  novel  manner.  In  the  space 
70 


FROM    THE    PRACTICAL    VIEWPOINT 


71 


THE    PASTEURIZATION    OF    MILK 

between  the  inner  and  outer  shell,  there  are  placed 
near  the  top  two  perforated  pipes,  into  which  hot 
water  is  forced.  The  water  is  thrown  through 
the  perforations,  in  jets,  against  the  outer  surface 
of  the  inner  shell.  It  flows  down,  following  the 
contour  of  the  tank,  and  drops  from  the  bot- 
tom, from  whence  it  is  again  pumped  through 
the  pipes  after  being  reheated.  The  milk  in  the 
meantime  is  kept  in  agitation  by  means  of  the 
paddles. 

In  any  of  these  tanks  it  usually  requires  from 
fifteen  minutes  to  twenty-five  minutes  to  raise  the 
milk  from  50°  to  a  temperature  of  145°.  The 
proper  temperature  having  been  attained,  the  steam 
is  shut  off,  and  the  milk  is  allowed  to  remain  hot 
in  the  tank  for  any  desired  length  of  time. 

The  tank  form  of  pasteurizer  in  practice  shows 
excellent  results.  In  plants  where  there  are  large 
quantities  of  milk  to  be  pasteurized  it  is  necessary 
that  two,  three  or  more  tanks  be  arranged  in  se- 
ries. This  insures  a  continuous  flow  of  milk 
through  the  cooling  apparatus  and  the  filling  de- 
vices. In  actual  operation  with  three  tanks,  it 
occurs  that  while  one  tank  is  being  emptied  after 
heating  and  holding,  the  milk  is  being  held  in  the 

72 


FROM    THE    PRACTICAL    VIEWPOINT 

second  tank,  while  in  the  third  tank  the  milk  is 
flowing  in  and  is  being  heated.  These  operations 
are  repeated  in  rotation. 

Many  tests  have  shown  that  if  the  water  in  the 
heating  coils  is  heated  by  injecting  steam  directly 
into  the  heating  coil,  the  temperature  at  the  inlet 
end  is  rarely  above  165°.  It  may  occasionally 
reach  175°.  Usually  it  is  sufficiently  low  so  that 
the  milk  is  not  injured  by  superheating.  It  can  be 
readily  seen  that  the  temperature  at  the  inlet  end 
of  the  coil  is  much  greater  than  at  the  outlet  end, 
since  the  cold  milk  takes  up  the  heat,  therefore  the 
heating  efficiency  of  the  coil  is  not  equally  great 
for  its  entire  length.  Some  attempts  have  been 
made  to  improve  matters  by  placing  a  smaller  per- 
forated coil  inside  the  larger  pipe,  so  that  the 
water  distributed  through  the  coil  would  have  the 
same  temperature  in  its  entire  length. 

An  objection  to  the  submerged  coil  is  that  it  be- 
comes necessary  to  have  the  bearings  packed  with 
some  sort  of  a  stuffing-box.  Stuffiing-boxes  are 
always  a  source  of  possible  danger  both  on  account 
of  the  absorption  of  milk,  which  renders  cleaning 
difficult,  and  on  account  of  the  fact  that  the  con- 
stant attrition  of  the  metal  at  the  point  of  bearing 

73 


THE    PASTEURIZATION    OF    MILK 

creates  a  condition  whereby  a  metallic  taste  may 
be  imparted  to  the  milk. 

In  the  form  shown  in  Fig.  15  the  objections 
due  to  uneven  heat  distribution  are  at  least  partly 
overcome,  since  the  heat  is  the  same  at  both  ends 
and  on  both  sides  of  the  tank. 

In  Figs.  15  and  16  there  are  no  bearings  in  the 
milk,  and  stuffing-boxes  are  therefore  eliminated. 

It  is  obvious  that  when  pumps  of  large  capacity 
force  the  water  rapidly  through  the  coils,  the  tem- 
perature will  be  more  nearly  uniform  throughout 
the  entire  length,  and  a  lower  initial  temperature 
can  be  employed. 

In  plants  where  a  comparatively  small  amount 
of  milk  is  to  be  pasteurized,  as  frequently  occurs 
in  country  shipping  stations,  one  or  two  tanks  will 
hold  all  the  milk  which  is  received  at  a  plant  each 
day.  It  is  therefore  possible  to  use  the  tank  for 
several  purposes.  First,  as  a  dumping  tank  for 
receiving  the  milk;  second,  as  a  heater;  third,  as 
a  holding  apparatus;  fourth,  as  a  cooler,  since  by 
replacing  the  hot  water  by  ice  water  or  brine  in 
the  coils,  the  milk  can  be  cooled  in  the  same  tank. 
Fifth,  cans  can  be  filled  directly  from  these  tanks. 
In  using  the  tank  as  a  cooler,  however,  it  is  found 
74 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  16 


75 


THE    PASTEURIZATION    OF    MILK 

that  the  time  required  is  usually  considerably  over 
thirty  minutes,  which  is  longer  than  most  authori- 
ties will  allow.  In  some  instances  the  writer  has 
found  that  from  an  hour  to  an  hour  and  a  half 
was  required.  Where  brine  can  be  circulated  rap- 
idly through  the  coil,  this  time  can  be  considerably 
reduced,  especially  if  the  coil  is  large.  Some  spe- 
cial tanks  are  provided  with  unusually  large  coils. 
In  plants  which  are  at  a  considerable  distance 
from  the  point  where  the  milk  is  consumed,  the 
tank  system  of  pasteurizing  has  this  added  advan- 
tage. It  is  not  always  possible  to  get  the  milk  into 
the  creamery  from  the  patrons  and  to  pasteurize 
it  before  the  departure  of  the  milk  train.  In  some 
localities  the  regulations  of  the  authorities  specify 
that  pasteurized  milk  must  be  sold  within  from 
twenty-four  to  thirty-six  hours  after  pasteuriza- 
tion. At  these  distant  points  it  therefore  becomes 
necessary  to  hold  over  some  raw  milk  from  day  to 
day.  If  a  pasteurizing  system  other  than  the  tank 
system  is  employed,  this  raw  milk  is  stored  in 
cans,  and  a  considerable  amount  of  extra  labor  is 
required  to  handle  them.  If  the  tank  is  used,  the 
milk  which  is  received  on  one  day  may  be  placed 
in  the  tank  and  there  stored  till  the  following 
76 


FROM    THE    PRACTICAL    VIEWPOINT 

morning,  it  being  kept  cold  in  the  meantime  by 
the  circulation  of  cold  water  through  the  coils. 
This  milk  may  be  heated  on  the  morning  of  pas- 
teurization as  early  as  necessary  to  get  it  ready 
for  shipment,  no  handling  or  transfer  of  the  milk 
being  previously  necessary. 

In  case  the  tank  is  used  as  both  a  heater  and  a 
cooler,  there  is  of  course  a  considerable  strain 
upon  the  joints  of  the  apparatus  due  to  the  expan- 
sion and  contraction  of  the  metal.  Those  forms  of 
apparatus  are  therefore  the  most  desirable  which 
are  the  most  strongly  constructed,  and  are  there- 
fore least  liable  to  break.  A  coil  of  pipe  is 
stronger  than  a  screw  disc. 

Fifth  Type. — Another  procqss  which  has  been 
used  to  a  limited  extent  for  pasteurized  milk  is 
known  as  bottle  pasteurizing.  By  this  method,  the 
bottles  are  filled  with  cold  milk  and  are  hermeti- 
cally sealed.  They  are  then  either  placed  in  a 
tank,  where  they  are  submerged  in  water,  or  else 
they  are  carried  under  showers  of  water.  In  either 
case  the  temperature  of  the  water  increases  as 
the  bottles  are  carried  forward.  When  the  de- 
sired temperature  is  reached,  the  bottles  are  then 
held  for  the  desired  time  and  are  then  brought 
77 


THE    PASTEURIZATION    OF    MILK 

in  contact  with  cold  water,  either  in  tanks  or 
in  showers,  till  the  temperature  is  sufficiently 
reduced. 

There  is  little  doubt  that  from  the  purely  theo- 
retical point  of  view  the  pasteurization  of  milk  in 
the  bottle  is  the  ideal  method.  During  the  process 
not  only  the  bacteria  contained  in  the  milk  are  de- 
stroyed, but  also  whatever  bacteria  may  have  been 
contained  in  the  bottles  and  on  the  caps  are  also 
killed.  It  can  also  be  seen  that  the  danger  of 
recontamination  after  pasteurization  is  reduced  to 
the  minimum. 

There  are  several  forms  of  apparatus  on  the 
market  in  which  the  pasteurization  takes  place  in 
the  bottle,  two  of  which  are  shown  in  Figs.  17  and 
18.  This  method  of  treatment  is  very  extensively 
used  in  the  manufacture  of  beer.  In  Fig.  17,  the 
cases  filled  with  bottles  of  the  milk  are  carried  by 
an  endless  chain  conveyor  through  several  tanks 
of  water  in  succession.  The  water  in  the  first  tank 
is  warm,  is  hotter  in  the  next,  and  so  on  tili  the 
maximum  is  reached,  after  which  the  milk  is  car- 
ried into  the  cooling  tanks.  The  entire  process 
requires  an  hour  or  more.  • 

In  the  process  shown  in  Fig.  18,  an  endless  plat- 
78 


FROM    THE    PRACTICAL   VIEWPOINT 


FIG.  17 
79 


THE    PASTEURIZATION    OF    MILK 


FIG.  18 


form  carries  the  cases  of  bottles  under  showers  of 
water,  of  varying  temperatures. 

When  milk  is  pasteurized  by  this  method,  a  more 
complete  cooling  is  necessary  than  is  the  case  with 
80 


FROM    THE    PRACTICAL    VIEWPOINT 

beer.  More  cooling  tanks  or  additional  showers 
are  therefore  required. 

In  a  rather  new  machine,  not  shown  in  this  book, 
the  bottles  are  placed  in  a  thoroughly  insulated  box 
or  compartment,  where  they  are  subjected  to  a 
shower  of  water,  the  temperature  of  which  is  in- 
creased or  decreased  at  will  by  proper  regulating 
devices  on  the  outside  of  the  apparatus.  It  is 
claimed  that  with  this  outfit  the  heating  and  cool- 
ing is  rapidly  accomplished,  and  that  the  com- 
plete insulation  of  the  compartment  prevents  the 
loss  of  heat.  It  is  also  said  that,  for  the  same  rea- 
son, the  same  apparatus  can  be  used  as  a  cold 
storage  box,  and  the  treated  milk  can  be  allowed 
to  remain  in  the  apparatus  after  the  completion 
of  the  process  till  it  is  ready  to  be  taken  out  for 
delivery.  These  claims  would  seem  to  make  it  an 
especially  desirable  outfit  for  small  dealers,  and 
for  dairymen  in  or  near  the  cities  where  the  milk 
is  to  be  sold. 

The  objections  which  are  advanced  against 
the  process  of  bottle  pasteurization  are,  first,  that 
the  cap  which  it  is  necessary  to  use  upon  the  bot- 
tles in  order  to  secure  a  tight  seal  is  expensive; 
too  much  so  to  warrant  its  use  upon  milk  which  is 
81 


THE    PASTEURIZATION    OF    MILK 

sold  at  the  popular  price.  It  can,  however,  be 
used  on  bottles  containing  milk  sold  at  advanced 
prices,  like  Certified  Milk,  Grade  A,  etc.  The 
second  objection  is  that  since  the  milk  expands 
upon  being  heated,  the  bottles  cannot  be  entirely 
filled.  The  bottles  must  therefore  be  made  of  a 
size  especially  large,  and  customers  must  be 
taught  that  bottles  which  are  not  full  do  still  in 
fact  contain  the  full  measure  of  milk.  A  third 
objection  advanced  has  been  that  milk  in  bottles 
which  are  not  full  is  more  likely  to  become  shaken 
up,  and  the  cream  disturbed,  than  is  the  case  in 
bottles  completely  filled.  This  objection  is 
probably  not  of  serious  moment.  A  fourth  and 
rather  serious  objection  is  that  the  expense  in  the 
consumption  of  heat  units  is  much  greater  than 
when  other  methods  of  pasteurizing  are  employed. 
The  reason  for  this  is  that  the  mass  of  glass  in 
the  bottle  nearly  equals  the  mass  of  the  milk,  and 
that  since  both  bottle  and  milk  must  be  heated 
and  also  cooled,  nearly  double  the  amount  of  heat 
is  necessary,  and  a  proportionately  great  amount 
of  cooling  medium  is  used.  In  large  plants  this 
added  expense  is  very  considerable. 

An  attempt  has  been  made  to  overcome  this  last 
82 


FROM    THE    PRACTICAL    VIEWPOINT 

objection,  in  part  at  least,  by  providing  a  series 
of  tanks  shown  in  Fig.  19.  The  five  tanks  shown 
in  line  No.  1,  2,  3,  4,  5  are  used  for  containing 
the  cases  of  filled  bottles  which  are  to  be  heated. 
These  are  lowered  into  the  tanks  by  suitable  de- 
vices. The  other  three  tanks  behind  the  pas- 
teurizing tanks  contain  the  water  to  be  used  in  the 
process.  One,  A,  contains  hot  water,  which  is 
kept  at  a  constant  temperature  by  means  of  a 
thermostat.  From  this  tank  the  water  is  circu- 
lated by  means  of  a  pump  through  the  tank,  which 
at  the  time  contains  the  bottles  which  are  being 
heated  and  held. 

A  second  tank,  C,  contains  cold  water,  which  is 
kept  cold  either  by  ice  or  by  a  brine  coil.  This 
water  is  circulated  by  a  pump  through  the  pas- 
teurizing tank,  in  which  at  the  time  are  contained 
the  bottles  which  were  being  cooled. 

The  third  tank,  C,  is  called  a  tempering  tank. 
The  water  in  this  is  used  for  regenerative  pur- 
poses, in  the  following  manner:  After  a  tank  full 
of  bottles  has  been  heated  and  held  for  the  de- 
sired length  of  time,  the  hot  water  is  all  returned 
to  the  heating  tank,  rendering  the  bottle  tank 
empty  of  water.  Cool  water  from  the  tempering 
83 


THE    PASTEURIZATION    OF    MILK 

tank  is  then  admitted.  This  cools  the  hot  bottles 
of  milk  to  a  certain  extent,  and  is  in  turn  partly 
heated.  The  water  is  then  returned  to  the  tem- 
pering tank,  after  which  the  cold  water  from  tank 
C  is  pumped  into  the  tank  full  of  partially  cooled 
bottles,  and  when  the  cooling  is  complete,  the  bot- 
tles are  removed,  and  the  tank  is  filled  with  fresh, 
unpasteurized  bottled  milk.  The  warm  water  from 
the  tempering  tank,  then  being  admitted,  it  begins 
to  warm  the  cold  bottles  and  is  itself  cooled. 
After  its  return  to  the  tempering  tank  it  is  ready 
to  be  used  again  in  the  routine  which  has  been 
described,  the  process  being  repeated  indefinitely. 
In  this  way  a  large  amount  of  heat  is  saved  which 
would  be  otherwise  wasted. 

From  the  illustration  and  the  description  the  im- 
pression is  gained  that  this  apparatus  would  be 
rather  cumbersome  to  operate,  although  it  would 
no  doubt  be  possible  to  somewhat  simplify  the  me- 
chanical arrangements  for  shifting  the  water  from 
tank  to  tank.  The  writer  is  not  personally  fa- 
miliar with  any  plant  where  such  an  arrangement 
is  in  use. 

Another  method  has  been  devised  for  saving 
some  of  the  heat  otherwise  wasted.  This  consists 
84, 


FROM    THE    PRACTICAL    VIEWPOINT 


.rH 
1*1 


85 


THE    PASTEURIZATION    OF    MILK 

in  heating  the  milk  in  any  good  form  of  pasteuriz- 
ing apparatus,  and  then  pouring  it,  while  hot,  into 
bottles  which  have  just  emerged  in  a  hot  condition 
from  this  sterilizing  apparatus.  The  heat  which 
is  usually  lost  in  cooling  the  hot  bottles  is  in  this 
way  saved.  Since,  however,  the  bottles  must  in 
any  case  be  cooled,  it  can  be  seen  that  the  cooling, 
which  usually  takes  place  slowly  in  the  air  when 
washed  bottles  are  stored  in  the  ordinary  way, 
must  now  be  accomplished  rapidly  in  order  to  re- 
duce the  milk  to  the  proper  temperature  in  the 
time  required.  This  necessitates  the  use  of  ice 
water  or  brine  refrigeration,  and  since  the  volume 
of  glass  used  equals  the  volume  of  the  milk,  dou- 
ble the  amount  of  cooling  medium  is  required  than 
when  only  the  milk  is  cooled. 

Experiments  were  made  by  Ayers  and  Johnson 
in  which  the  heated  milk  in  bottles  received  a  pri- 
mary cooling  by  means  of  blasts  of  air  at  ordinary 
temperatures.  These  experiments  indicated  that 
a  considerable  economical  saving  of  cooling  medium 
thus  could  be  effected.  Completing  the  cooling  by 
means  of  blasts  of  chilled  air  produced  satisfac- 
tory results.  The  fact  that  the  cooling  process 
required  a  long  time  seemed  to  produce  no  harm- 
86 


FROM    THE    PRACTICAL    VIEWPOINT 

f ul  effects  upon  the  milk.  There  was  no  noticeable 
increase  in  bacterial  content  when  the  cooling  was 
accomplished  within  two  hours.  These  results 
were  obtained  under  conditions  which  somewhat 
approached  what  might  be  termed  laboratory  sur- 
roundings, and  it  is  possible  that  under  the  stress 
of  commercial  conditions,  difficulties  of  operation 
might  develop  which  would  unfavorably  influence 
the  results. 

There  is  one  objection  which  has  been  raised  in 
the  practice  of  pasteurization  in  the  bottle  which 
may  have  some  weight  in  certain  circumstances. 
It  is  claimed  that  because  of  the  fact  that  the  bot- 
tles are  tightly  sealed,  there  is  no  chance  for  the 
escape  of  disagreeable  or  offensive  odors.  In  other 
heating  and  cooling  processes,  a  certain  amount  of 
aeration  takes  place,  with,  as  claimed  by  some 
dealers,  beneficial  results.  "Those  who  advocate 
bottle  pasteurization  claim  that  during  the  process 
of  heating,  the  objectionable  gases  are  driven  out 
of  the  milk  and  are  forced  beneath  the  bottle  cap 
into  the  outer  air.  In  so  far  as  known  to  the 
writer,  the  correctness  of  this  claim  has  not  been 
demonstrated.  Neither  is  it  known  that  objec- 
tionable odors  or  flavors  have  been  subjects  of 
87 


THE    PASTEURIZATION    OF    MILK 

complaint  among  the  users  of  milk  pasteurized  in 
the  bottle. 

An  objection  which  may  be  a  serious  one  at 
times  is  this.  If  the  bottle  caps  are  not  abso- 
lutely tight,  as  may  occur  when  bottle  necks  are 
chipped  or  uneven,  there  is  an  opportunity  for 
water  to  be  drawn  into  the  bottle.  When  the  cooling 
is  being  carried  on  there  is,  of  course,  a  partial 
vacuum  produced  in  the  space  above  the  milk,  and 
if  in  cooling  the  bottles  are  immersed  in  water, 
then  the  water  might  be  drawn  into  the  bottle.  If 
the  water  were  impure  the  danger  becomes  ap- 
parent. 

A  certain  advantage  in  the  use  of  the  bottle  pas- 
teurizing process  from  a  commercial  point  of  view 
becomes  apparent  when  only  small  amounts  of 
milk  are  to  be  treated.  If  individual  dairies  are 
compelled  by  legal  requirements  to  pasteurize  the 
milk  sold,  it  is  a  comparatively  inexpensive  mat- 
ter to  equip  for  pasteurizing  in  the  bottle.  The 
only  equipment  necessary  is  a  tank  large  enough 
to  immerse  the  filled  bottles;  facilities  for  supply- 
ing hot  water  to  the  tank,  and  also  for  replacing 
the  hot  water  with  cold  when  the  heating  is  ac- 
complished. Heat-recording  devices  are  manu- 
88 


FROM    THE    PRACTICAL    VIEWPOINT 

factored  for  use  in  connection  with  bottle  pasteuriz- 
ing. When  this  method  is  installed  in  small  dairies 
there  is  saved  the  expense  of  installing  heaters, 
holders,  coolers,  pumps  and  piping.  Equally  im- 
portant to  the  dairyman  is  the  fact  that  the  oper- 
ating expenses  are  less,  since  the  amount  of  ma- 
chinery to  be  kept  cleaned  and  in  repair  is  almost 
nothing. 

A  process  of  pasteurizing  which,  so  far  as  known 
to  the  writer,  has  been  but  little  employed,  con- 
sists in  making  use  of  the  vacuum  pans  which  are 
commonly  employed  in  the  manufacture  of  con- 
densed milk.  With  certain  changes,  these  can  be 
used  satisfactorily  in  pasteurizing  milk.  As  usu- 
ally constructed,  these  vacuum  pans  are  retort- 
shaped  structures  made  of  copper,  and  contain  at 
the  bottom  two  or  three  coils  of  copper  pipe,  into 
which  live  steam  is  admitted.  When  milk  is  con- 
densed, these  hot  pipes  raise  the  milk  to  the  de- 
sired temperature,  and  the  natural  water  contained 
in  the  milk  is  drawn  off  in  the  form  of  steam  by 
means  of  the  vacuum  pipe  attached  to  the  top  of 
the  pan.  If  these  pans  are  used  without  change 
as  pasteurizing  tanks,  it  is  probable  that  the  live 
steam  in  the  heating  coils  would  have  a  tendency 
89 


THE    PASTEURIZATION    OF    MILK 

to  scorch  the  milk,  and  it  would  be  necessary  to 
replace  the  steam  by  hot  water,  which  should  be 
rapidly  pumped  through  the  coils,  the  water  being 
maintained  at  a  uniform  temperature  in  tanks  out- 
side the  condensing  pan.  The  pans  could  be  used 
also  for  holding  the  milk  after  it  is  heated  for  any 
desired  length  of  time. 

In  plants  where  seasonal  conditions  require  that 
the  milk  be  used  for  different  purposes  at  different 
times  of  the  year,  such  an  arrangement  would 
effect  a  saving  of  expense  in  equipment,  and 
would  thus  aid  in  obtaining  greater  operating  effi- 
ciency. 

From  time  to  time  attempts  are  made  to  bring 
forward  some  new  process  for  treating  milk  de- 
signed to  reduce  the  number  of  bacteria  in  milk 
by  some  agency  other  than  heat.  One  of  these  is 
the  treatment  of  milk  by  means  of  an  electric  cur- 
rent. In  one  electric  process,  the  milk  is  allowed 
to  flow  from  chamber  to  chamber  through  orifices 
of  small  diameter.  While  so  flowing  it  is  sub- 
jected to  a  strong  alternating  current  of  electricity. 
It  is  claimed  that  this  current  destroys  the  bac- 
teria contained  in  the  milk  through  the  shock  to 
which  they  are  subjected,  and  that  the  digestive 
90 


FROM    THE    PRACTICAL    VIEWPOINT 

qualities   of  the   milk   are   not   impaired,   but  are 
rather  improved. 

It  is,  however,  found  necessary  to  heat  the  milk 
to  about  130°  before  subjecting  it  to  the  electric 
current,  and  during  electric  treatment  it  attains  a 
temperature  of  about  158°,  due  to  the  resistance 
of  the  milk  to  the  electric  discharge.  It  is  an 
open  question  whether  the  destruction  of  bacterial 
life,  which  undoubtedly  takes  place,  is  due  to  the 
electric  current  or  to  the  heat  to  which  the  milk  is 
subjected.  The  results  of  tests  made  of  the  milk 
so  treated  indicate  that  the  percentage  of  bacteria 
destroyed  is  high.  If  the  effectiveness  of  the  appa- 
ratus depends  upon  the  heat  generated  during  the 
process,  it  is  probable  the  high  percentage  of  bac- 
terial destruction  is  partially  due  to  the  fact  that 
milk  flows  in  such  a  small  stream  through  the  ma- 
chine. Every  portion  of  it  is  thus  uniformly 
heated  to  the  maximum  temperature,  and  even 
when  milk  is  not  held  for  any  appreciable  length 
of  time,  it  has  been  found  in  laboratory  tests  that 
the  bacteria  are  killed.  As  before  stated,  it  is  a 
fact  that  mechanical  defects  which  exist  in  all  ma- 
chinery render  it  difficult  to  maintain  uniform  tem- 
peratures. This  makes  the  holding  of  hot  milk  a 

91 


THE    PASTEURIZATION    OF    MILK 

necessary  requirement  in  order  to  equalize  tem- 
peratures. 

The  ultra-violet  rays  have  been  suggested  as  a 
means  of  killing  bacteria  in  milk.  Since,  however, 
these  rays  have  but  little  penetrating  power,  it  has 
been  found  that  the  opaque  character  of  milk  pre- 
vents obtaining  the  good  results  which  have  re- 
sulted in  the  use  of  the  ultra-violet  rays  in  water 
purification. 

The  ozone  process,  which  will  by  oxidation  de- 
stroy some  forms  of  bacterial  life,  and  which  will 
destroy  odors,  also  acts  upon  the  constituent  parts 
of  milk  and  so  changes  them  that  it  seems  probable 
that  ozone  can  never  be  satisfactorily  substituted 
for  the  usual  pasteurization  process. 

An  ingenious  idea  has  been  brought  to  the 
writer's  attention  by  which  it  was  proposed  to  de- 
stroy the  bacteria  by  treatment  in  vacuum.  It  is 
well  known  that  when  persons  work  under  abnor- 
mally high  air  pressure  as  in  tunnel  construction 
under  rivers,  etc.,  it  is  necessary  for  them  to  exer- 
cise the  greatest  care  in  coming  out  into  the  normal 
air  pressure.  The  air,  which  under  pressure  is 
absorbed  in  the  bodily  tissues,  suddenly  expands 
when  the  abnormal  pressure  is  relieved.  The  cells 

92 


FROM    THE    PRACTICAL    VIEWPOINT 

of  the  body  may  be  strained  or  broken.  In  such 
case  the  disease  known  as  "the  bends"  results.  It 
has  been  proposed  that  a  machine  might  be  so  con- 
structed that  an  abnormal  air  pressure  upon  the 
milk  could  be  suddenly  released,  thus  allowing  the 
air  within  the  germ  bodies  to  quickly  expand  and 
so  destroy  them.  No  such  system  has  been  made 
commercially  available. 


CHAPTER    III 

HOLDERS 

As  previously  stated,  the  New  York  City  De- 
partment of  Health  was  the  pioneer  among  health 
authorities  to  require  that  milk,  in  order  to  be  offi- 
cially considered  to  be  pasteurized,  must  be  held, 
after  heating  for  a  definite  length  of  time.  When 
this  regulation  was  adopted  no  holding  device  was 
upon  the  market  which  was  suitable  to  be  used  on 
a  commercial  basis.  Since  that  time  most  of  the 
manufacturing  firms  making  milk-handling  ma- 
chinery have  constructed  and  placed  upon  the  mar- 
ket one  or  more  forms  of  holding  apparatus.  These 
differ  in  detail,  and  to  a  considerable  extent  in  the 
efficiency  with  which  they  operate.  In  general, 
however,  it  may  be  said  they  are  naturally  divided 
into  two  classes: 

First,  those  which  may  be  termed  absolute 
holders,  and 

Second,  those  which  are  of  the  continuous  or 
flow  type. 

Absolute  Holders 

The  absolute  holders  are  so  called  for  the  rea- 
son that  the  milk,  after  being  heated,  is  all  held 


FROM    THE    PRACTICAL   VIEWPOINT 

in  tanks  or  compartments  for  a  definite  length  of 
time  before  being  discharged. 

The  first  holder  placed  upon  the  market  was  of 
this  character,  and  consisted  of  an  upright  cylin- 
drical tank  having  partitions  radiating  from  the 
centre,  thus  dividing  the  tank  into  eight  compart- 
ments. Such  a  holding  apparatus  is  illustrated  in 
Fig.  20.  The  drawing,  however,  shows  a  later 
type  of  the  same  apparatus,  in  which  there  are 
eight  separate  tanks  which  are  arranged  in  a  cir- 
cle. An  upright  shaft  extends  through  the  centre 
of  the  tank  or  the  group  of  tanks,  as  the  case 
may  be,  to  which  is  attached,  at  the  upper  end,  a 
revolving  spout,  into  which  the  milk  is  discharged 
through  the  pipe  from  the  heater.  This  spout  as 
it  revolves  causes  each  tank  to  be  filled  in  turn. 
To  each  tank  is  attached  at  the  bottom  an  outlet 
pipe  and  valve.  These  valves  are  kept  closed  by 
springs,  and  are  opened  by  means  of  a  revolving 
arm,  or  cam,  attached  to  the  lower  end  of  the  up- 
right shaft  before  referred  to.  These  outlet  pipes 
discharge  into  a  common  pipe,  through  which  the 
milk  is  conveyed  to  the  cooler.  By  placing  the 
revolving  inlet  spout  in  proper  position  with  rela- 
tion to  the  revolving  cam  at  the  bottom,  it  can  be 
95 


THE    PASTEURIZATION    OF    MILK 

readily  seen  that  each  tank  will  be  emptied  after 
the  milk  has  been  held  in  the  tank  during  the  time 
required  for  the  shaft  to  make  a  complete  revolu- 
tion. By  properly  gearing  the  mechanism  which 
operates  the  shaft  it  can  be  seen  that  the  time  of 
holding  can  be  fixed  at  will  for  any  period  de- 
sired. A  little  thought,  however,  will  make  it  clear 
that  the  actual  holding  time  will  not  equal  the  time 
required  for  the  shaft  to  make  a  complete  revolu- 
tion, since  approximately  one-eighth  of  this  time 
is  occupied  in  filling  each  tank,  and  one-eighth  is 
required  to  discharge  each  tank.  In  order  to  ar- 
rive at  the  actual  minimum  time  for  which  we  can 
be  sure  all  the  milk  is  held,  we  must  reduce  the 
time  of  revolution  by  one-fourth,  or  25  per  cent. 
Thus  if  it  is  desired  to  hold  the  milk  for  thirty 
minutes,  it  is  necessary  that  the  time  of  revolution 
of  the  operating  shaft  be  forty  minutes,  which 
reduced  by  25  per  cent,  equals  thirty  minutes,  the 
actual  holding  time. 

It  is  also  necessary  to  make  sure  that  the  dis- 
charge pipes  are  completely  closed  before  the  milk  is 
allowed  to  enter  through  the  inlet  pipe  into  any  tank. 
Otherwise  some  milk  may  pass  out  of  the  holder 
without  being  held  for  any  definite  length  of  time. 
96 


FROM    THE    PRACTICAL    VIEWPOINT 


97 


THE    PASTEURIZATION    OF    MILK 

Another  point  to  be  observed  when  partitions 
separate  the  tanks  is  to  make  sure  that  no  tank 
becomes  filled  to  overflowing.  In  such  case,  the 
milk  will  flow  into  a  tank  from  which  milk  is  be- 
ing discharged,  and  thus  the  holding  time  becomes 
a  matter  of  great  uncertainty. 

In  this  form  of  holder  considerable  foam  de- 
velops, due  to  the  dropping  of  the  milk  for  a  con- 
siderable distance  from  the  discharge  pipe  into 
the  body  of  milk  in  the  tanks.  The  foamy  milk 
does  not  retain  the  heat  as  well  as  is  desirable, 
and  as  a  consequence  the  destruction  of  the  bac- 
teria is  not  always  sufficiently  complete. 

In  Fig.  21  the  eight  compartments  or  wells  are 
themselves  immersed  in  a  tank  of  water,  the  tem- 
perature of  which  is  kept  somewhat  above  that  to 
which  the  milk  is  heated.  In  this  form  of  appa- 
ratus the  tendency  to  foam  is  largely  overcome 
from  the  arrangement  which  allows  the  milk  to 
enter  the  well  from  the  bottom.  Both  the  inlet 
pipe  and  the  outlet  pipe  are  operated  by  means  of 
mechanism,  which  is  above  the  tanks.  There  are 
sixteen  valves,  each  of  which  is  made  tight  by  a 
ground  seat,  upon  which  the  valve  sets.  These 
valves  are  at  the  lower  end  of  the  plug  shanks, 
98 


FROM    THE    PRACTICAL    VIEWPOINT 


THE    PASTEURIZATION    OF    MILK 

which  extend  through  the  milk  to  the  top  of  the 
tanks.  Any  loosening  of  these  valves,  or  any  in- 
accurate adjustment  of  the  cams  which  operate 
them,  may  cause  milk  to  be  discharged  from  a  tank 
before  it  has  been  held  a  proper  length  of  time. 
The  efficiency  of  the  apparatus  would  thus  be 
impaired. 

The  fact  that  the  temperature  of  the  heated 
milk  is  not  reduced  during  the  holding  process 
appears  to  be  an  advantage.  The  surrounding 
jacket  of  hot  water  maintains  or  increases  the 
temperature  of  the  milk  in  the  vats. 

In  Fig.  22  the  eight  tanks  are  arranged  in  a 
circle  upon  a  frame  or  platform,  which  itself  re- 
volves, carrying  the  tanks  with  it.  A  central  tank, 
which  is  stationary,  receives  the  milk  from  the 
heater.  From  this  tank  the  milk  is  distributed  to 
the  various  holding  tanks  by  means  of  pipes, 
which  radiate  from  a  central  valve  beneath  the  re- 
ceiving tank.  This  single  central  valve  is  of  very 
ingenious  construction,  and  is  so  made  that  all  the 
holding  tanks  are  filled  and  are  also  discharged 
through  the  same  valve.  Thus  it  is  seen  that  this 
one  valve  replaces  the  sixteen  valves  which  are 
employed  in  such  an  apparatus  as  shown  in  Fig. 
100 


FROM    THE    PRACTICAL 


101 


THE    PASTEURIZATION    OF    MILK 


FIG.  22-B 


21.      The    chances    of   valve    difficulties    are    thus 
reduced. 

The  arrangement  of  this  valve  is  rather  diffi- 
cult to  describe.  It  is  shown  in  Fig.  22-B.  A 
central  core  is  attached  to  the  pipe,  which  de- 
scends into  it  from  the  central  tank.  This  core 
remains  stationary,  and  is  provided  with  a  sin- 
gle opening,  which  is  a  continuation  of  and  is  at 
right  angles  to  the  discharge  pipe  from  the  tank 
102 


FROM    THE    PRACTICAL    VIEWPOINT 

above  it.  Outside  this  core,  and  closely  fitting 
it,  is  a  shell  which  revolves  around  it.  Into  this 
shell  the  eight  pipes  from  the  various  holding 
tanks  are  fastened,  and  they  are  so  placed  that  as 
the  shell  revolves  each  pipe  is  in  turn  brought  op- 
posite to  the  opening  into  the  inner  core.  The 
milk  is  thus  admitted  to  the  bottom  of  each  hold- 
ing tank  in  turn.  As  the  shell  continues  to  re- 
volve each  pipe  in  the  outer  shell  passes  in  turn  the 
inner  opening  and  the  milk  supply  is  thus  shut  off 
from  each  particular  tank,  and  so  remains  until  the 
shell  has  nearly  completed  its  revolution.  The  pipe 
opening  from  the  holding  tank  then  comes  oppo- 
site to  another  opening  in  the  inner  core,  which 
extends  only  a  short  distance  into  the  core.  This 
opening  turns  downward  and  is  connected  with  a 
pipe,  which  discharges  the  milk  to  the  cooler.  Thus 
it  is  seen  that  each  tank  is  filled  in  turn  and  is  in 
turn  discharged  automatically.  The  same  method 
must  be  employed  for  arriving  at  the  minimum 
holding  time  as  that  used  with  the  device  illus- 
trated in  Fig.  20,  namely,  the  time  of  revolution 
must  be  reduced  by  25  per  cent. 

The  exact  holding  time  may  be  arrived  at  in 
another    way,    namely,    by    carefully    noting    the 
103 


THE    PASTEURIZATION    OF    MILK 

exact  time  at  which  the  last  milk  enters  any  sin- 
gle compartment  of  the  holder,  and  then  observ- 
ing the  exact  time  at  which  the  first  milk  flows 
from  the  same  tank.  The  difference  indicates  the 
minimum  holding  time.  Of  course,  some  of  the 
milk  is  held  for  a  longer  time  than  that  which  is 
thus  indicated,  but  we  are  sure  that  none  is  held 
for  a  less  time. 

It  will  be  found  that  the  time  as  observed  in 
this  way  is  nearly  equal  to  that  which  we  obtain 
by  calculation,  allowances  being  made  for  varia- 
tions in  the  mechanical  exactness  with  which  the 
machine  operates. 

It  will  be  seen  from  the  illustration  that  the 
various  holding  tanks  are  insulated  by  a  cork 
jacket,  so  that  little  heat  is  lost  during  the  hold- 
ing period.  It  will  be  noted,  however,  that  the 
pipes  leading  from  the  holding  tanks  to  the  cen- 
tral valve  are  not  insulated,  and  in  this  condition 
the  milk  which  lies  in  these  pipes  during  the  time 
of  revolution  may,  and  probably  will,  become 
cooled,  and  the  effectiveness  of  the  bacterial  de- 
struction will  be  impaired.  This  having  been 
brought  to  the  attention  of  the  manufacturers,  they 
provided  insulating  jackets  for  the  pipes  as  well 
104. 


FROM    THE    PRACTICAL    VIEWPOINT 

as  for  the  tanks.  Discharge  pipes  constructed  with 
these  insulating  jackets  are  now  provided  for  ma- 
chines which  are  placed  upon  the  market  at  the 
present  time. 

A  modification  of  this  type  of  holder  is  now  be- 
ing manufactured  in  which  the  holding  tanks  do 
not  revolve  but  are  made  stationary  and,  instead,  the 
central  valve  revolves.  The  same  effect  is  secured 
as  in  the  other  type,  and  there  is  this  advantage, 
that  less  power  is  required,  and  the  heavy  frame 
required  to  hold  the  revolving  tanks  is  not  neces- 
sary. There  is  also  this  added  advantage,  namely, 
that  a  small  plant  may  install  such  an  apparatus 
with  but  two  or  four  tanks,  and  as  business  ex- 
pands there  may  be  added  other  tanks,  it  being 
only  necessary  to  change  the  shell  of  the  valve 
which  revolves  about  the  core. 

In  Fig.  23  there  are  seven  oblong  enamel-lined 
tanks  which  are  immersed  in  a  tank  of  hot  water. 
These  are  each  filled  in  turn  by  me'ans  of  valves 
in  a  pipe  which  extends  along  the  upper  side  of 
the  series.  These  valves  are  opened  and  closed 
by  means  of  an  automatic  arrangement  operated 
by  a  revolving  shaft  extending  parallel  to  the  inlet 
pipe.  A  similar  shaft  extends  along  the  discharge 
105 


THE    PASTEURIZATION    OF    MILK 

pipe  at  the  bottom  of  the  series,  and  operates 
valves  which  automatically  regulate  the  discharge 
of  the  milk. 

There  is  one  thing  which  should  be  carefully  ob- 
served regarding  this  form  of  holder.  It  will  be 
noted  that  the  two  shafts  which  operate  both  the 
inlet  valves  and  the  outlet  valves  are  impelled  by 
a  single  worm-driven  gear.  Thus  both  shafts 
move  in  unison.  Care  must  be  taken  to  make  sure 
that  no  inlet  valve  is  opened  into  any  tank  till  the 
outlet  valve  is  completely  closed,  otherwise  some 
milk  will  flow  out  without  being  held  for  the 
proper  length  of  time. 

In  calculating  the  holding  time  with  this  appa- 
ratus, it  must  be  noted  that  since  there  are  but 
seven  tanks  in  the  series,  there  is  required  one- 
seventh  of  the  entire  period  of  sequence  for  each 
tank  to  fill  and  one-seventh  for  it  to  be  emptied. 
Thus  the  entire  time  of  sequence  must  be  reduced 
by  two-sevenths.  A  little  thought  will  make  it 
clear  that  as  the  number  of  tanks  in  a  series  de- 
creases in  number,  the  time  of  revolution  or  se- 
quence must  be  increased.  With  eight  tanks  a 
period  of  revolution  of  forty  minutes  reduced  by 
25  per  cent,  would  equal  thirty  minutes.  If,  how- 
106 


FROM    THE    PRACTICAL   VIEWPOINT 


107 


THE    PASTEURIZATION    OF    MILK 

ever,  a  seven-tank  holder  has  a  forty-minute  se- 
quence, which  is  reduced  by  two-sevenths,  we  have 
a  holding  time  of  but  twenty-eight  and  four- 
sevenths  minutes,  and  so  on  as  the  number  of 
tanks  decreases. 

A  modification  of  the  valve  system,  shown  in 
Fig.  23,  is  now  provided  by  the  manufacturers  of 
this  machine.  A  valve  exactly  similar  in  principle 
to  that  shown  in  Fig.  22-B  is  made  use  of.  All 
tanks  fill  and  empty  from  the  bottom,  thus  avoid- 
ing foam  and  reduring  the  danger  of  by-passing 
the  milk. 

All  the  types  of  holders  already  described  are 
being  used  with  very  satisfactory  results.  To 
summarize  the  points  which  should  be  observed 
in  either  buying  or  supervising  the  operation  of 
holders  of  this  character: 

First. — Any  serious  loss  of  heat  should  be  pre- 
vented by  complete  insulation  of  all  tanks  and 
pipes  in  which  the  heated  milk  is  held.  Of 
these  insulations,  the  hot-water  jacket  is  the  most 
expensive  and  perhaps  the  best.  There  is  a 
question  whether  the  added  expense  secures 
enough  added  efficiency  to  render  the  expenditure 
wise. 

108 


FROM    THE    PRACTICAL    VIEWPOINT 

Second. — We  should  be  sure  that  every  particle 
of  milk  is  held  for  the  minimum  time  required. 

Third. — The  valves  for  admitting  and  releasing 
the  milk  must  be  so  tightly  fitted  that  no  milk 
can  by  any  possibility  be  discharged  before  the 
proper  holding  time  is  completed.  It  may  be  pos- 
sible for  valves  to  become  so  worn  by  use  that 
annular  grooves  will  be  worn  around  them,  thus 
allowing  milk  to  be  by-passed  while  the  valve  is 
closed. 

Fourth. — Make  proper  calculation  to  determine 
that  the  cycle  of  filling,  holding  and  emptying  of 
the  tanks  is  long  enough  to  make  sure  that  the  hold- 
ing time  is  sufficient  and  in  addition  to  allow  for 
the  filling  and  emptying  of  the  tanks. 

Fifth. — Make  sure  that  the  inlet  valve  is  never 
open  into  a  tank  before  the  outlet  pipe  is  closed. 

Sixth. — Since  the  ease  and  convenience  of  clean- 
ing is  an  item  of  importance,  as  a  general  propo- 
sition it  may  be  said  that,  other  things  being  equal, 
a  machine  which  has  the  fewest  pipes  and  valves 
consistent  with  efficient  operation  is  the  most  de- 
sirable. 

Seventh. — It  is  desirable  that  as  little  foam  as 
possible  be  produced  in  the  operation  of  a  holder. 
109 


THE    PASTEURIZATION    OF    MILK 

Whatever  form  of  tank  holder  is  used,  it  is  nec- 
essary that  it  be  thoroughly  sterilized  before  use 
each  day,  by  the  admission  of  live  steam  for  a 
considerable  period  of  time.  This  sterilization  is 
of  importance  not  alone  for  the  destruction  of  the 
bacteria  contained  in  it,  but  also  in  order  that  the 
pipes  and  tanks  may  become  thoroughly  heated  im- 
mediately before  use.  If  they  are  not  so  heated, 
it  will  be  found  that  the  milk  first  admitted  to  the 
apparatus  will  be  considerably  cooled,  and  will  be 
discharged  at  a  temperature  much  below  that  re- 
quired by  the  regulations,  and  will  so  continue  until 
the  hot  milk  has  itself  slowly  heated  the  appa- 
ratus. This  may  require  fifteen  or  twenty  minutes. 
It  will  be  found  under  such  circumstances  that  the 
milk  first  discharged  from  a  holder  contains  many 
more  bacteria  than  that  which  flows  from  it  after 
the  machine  is  heated. 

Another  form  of  holder  which  belongs  to  the  ab- 
solute type  is  that  which  is  represented  by  the  tank 
heaters  shown  in  Figs.  11,  12,  13,  14,  14-B,  15,  16, 
and  previously  described.  In  these  the  milk,  after 
having  been  heated,  is  allowed  to  remain  for  any 
desired  length  of  time,  and  is  then  released.  This 
method  of  holding  has  produced  very  satisfactory 
110 


FROM    THE    PRACTICAL    VIEWPOINT 

results.  It  has  this  advantage;  that  the  milk 
comes  in  contact  with  no  new  metal  or  apparatus 
between  the  completion  of  the  heating  process  and 
the  time  when  the  milk  is  cooled.  One  disadvan- 
tage is  that  since  it  requires  considerable  time  for 
a  large  tank  full  of  milk  to  be  discharged,  the  last 
milk  leaving  the  tank  is  held  for  a  period  consid- 
erably longer  than  that  which  first  flows  from  it, 
and  this  long  holding  tends  to  interfere  with  the 
proper  rising  of  the  cream. 

Continuous  Holders 

The  continuous  or  flow  type  holders  differ  from 
the  absolute  holders  in  that  the  milk,  instead  of 
being  quietly  held  in  retainers  for  a  definite  length 
of  time  until  the  required  period  for  holding  is 
completed,  is  simply  retarded  in  its  flow.  This 
period  of  retardation  is  so  extended  that  before  the 
milk  passes  to  the  cooler  it  has  retained  its  tem- 
perature for  the  length  of  time  desired. 

There  are  several  forms  of  continuous  holders. 
One  of  the  first  of  these  is  the  so-called  Park 
holder,  invented  by  Dr.  William  H.  Park,  of  the 
New  York  City  Department  of  Health,  and  pat- 
Ill 


THE    PASTEURIZATION    OF    MILK 


FIG.  24 


ented  and  given  to  the  milk  trade  for  use  by  the 

inventor.      It  is   shown  in  Fig.   24,   and  consists 

primarily    of    an    upright    cylindrical    tank,    into 

112 


FROM    THE    PRACTICAL    VIEWPOINT 

which  the  milk  flows  at  the  top,  and  from  which 
it  is  discharged  at  the  bottom.  An  inverted  goose- 
neck attached  to  the  outlet  pipe  so  directs  the  out- 
flow that  no  milk  can  be  discharged  until  the  tank 
has  become  filled.  In  theory,  the  hot  milk  which 
enters  at  the  top  becomes  gradually  cooled  as  it 
flows  downward,  and  so  the  last  milk  to  enter  the 
tank  will  be  the  last  milk  to  leave  it.  If  this 
were  entirely  true,  then  the  time  required  for  fill- 
ing a  tank  would  be  identical  with  the  holding 
time.  In  such  case  the  various  particles  of  milk 
would  pass  through  the  tank  like  a  flock  of  sheep, 
one  after  another.  Unfortunately,  there  are  several 
disturbing  elements  which  enter  into  the  problem, 
and  the  particles  of  milk,  instead  of  resembling 
sheep,  more  nearly  resemble  a  flock  of  chickens 
in  their  behavior.  In  the  first  place,  the  milk 
which  is  nearest  to  the  outside  circumference  of 
the  tank  becomes  cooled  more  than  that  which  is 
in  the  centre,  and  as  it  cools  it  increases  in  weight, 
and  naturally  falls  to  the  bottom  and  goes  out. 
This  tendency  is  partly  overcome  by  providing  in- 
sulating jackets.  In  some  cases,  as  in  Fig.  25, 
the  jacket  is  a  hot-water  covering  contained  in 
the  space  between  the  inner  and  the  outer  shell. 
113 


THE    PASTEURIZATION    OF    MILK 

Again,  it  can  be  seen  that  if  the  temperature  of 
the  milk  as  it  enters  the  tank  from  the  heater  is 
not  accurately  controlled,  it  will  frequently  occur 
that  the  temperature  will  drop,  and  this  cooler  milk 
will  fall  through  the  body  of  milk  toward  the  bot- 
tom. It  is  also  true  that  the  force  of  the  milk  as 
it  enters  the  tank  from  the  heater  will,  unless  this 
force  is  broken,  tend  to  carry  the  milk  deeply  into 
the  body  of  that  already  in  the  tank,  and  so  cre- 
ate currents  which  will  interfere  with  the  actual 
holding  time.  This  force  is  broken  by  placing 
some  sort  of  a  baffle  plate  under  the  inlet  pipe. 
This  baffle  is  sometimes  so  arranged  that  it  floats 
on  the  surface  of  the  milk,  and  rises  as  the  tank 
becomes  filled.  In  other  cases  a  flat  piece  of 
metal  is  placed  near  the  top  of  the  tank,  and  may 
or  may  not  contain  perforations  which  allow  the 
milk  to  flow  through  as  well  as  over  the  edge  of 
the  plate.  It  is  immaterial  what  form  of  spreader 
is  used  so  long  as  the  currents  are  broken  up.  It 
will  be  seen  by  referring  to  the  illustration  that 
the  inverted  U-shaped  pipe  for  the  discharge  of 
the  milk  is  provided  with  a  by-pass  valve,  so  that 
the  tank  can  be  emptied  when  the  operation  is 
completed  for  the  day.  It  is  important  that  this 
114 


FROM    THE    PRACTICAL    VIEWPOINT 

U-pipe  be  provided  with  a  vent  at  the  upper  end, 
otherwise  a  syphon  will  be  created  and  the  milk 
will  all  be  rapidly  drained  from  the  tank. 

In  plants  where  a  large  amount  of  milk  is  pas- 
teurized, and  there  is  therefore  a  rapid  flow,  it  is 
necessary  to  install  more  than  one  of  these  tanks 
in  series,  and  in  some  instances  three  and  four 
tanks  are  so  installed,  each  succeeding  tank  being 
a  little  lower  than  the  one  before  it,  and  the  valves 
so  arranged  that  the  milk-flow  is  from  one  to  the 
other  through  the  entire  series.  This  also  helps 
to  equalize  any  uneven  temperature  which  may  oc- 
cur as  the  milk  is  discharged  into  the  first  tank. 

With  all  these  precautions  to  insure  a  steady 
and  even  flow,  it  is  never  safe  to  assume  that  the 
holding  time  is  correct  unless  a  test  is  made.  Only 
two  feasable  means  of  so  testing  the  tanks  have 
developed.  One  is  the  color  test  and  the  other 
the  temperature  test.  Neither  are  absolutely  ac- 
curate, but  are  sufficiently  so  for  practical  pur- 
poses. 

In  the  color  test,  the  tanks  are  filled  with  water, 

heated  to  the  same  temperature  as  is  the  case  when 

milk  is   pasteurized.      The  time  of   filling  having 

been   observed,   a   solution   of   some   intense   color, 

115 


THE    PASTEURIZATION    OF    MILK 

preferably  methylene  blue  or  uranin,  is  allowed 
to  flow  into  the  tank  with  the  heated  water.  The 
time  is  observed  between  the  time  of  its  introduc- 
tion and  the  time  when  the  first  trace  of  it  appears 
at  the  outlet.  In  order  to  make  the  test  as  ac- 
curate as  possible,  care  should  be  taken  that  a  com- 
plete solution  is  made  of  the  color,  otherwise  small 
particles  of  solid  color  may  fall  through  the  liquid 
and  deceive  the  observer.  The  solution  of  any 
color  is  of  course  slightly  heavier  than  the  liquid 
in  which  it  is  dissolved,  and  the  tendency  is  for 
it  to  fall  after  its  introduction.  Therefore,  the 
solution  should  be  made  as  nearly  as  possible  of 
the  same  specific  gravity  as  the  water  in  the  tank. 
If  it  can  be  made  slightly  less  in  weight  than  the 
water  the  result  of  the  test  will  be  rather  better. 
Even  with  the  greatest  care,  it  seldom  happens  that 
two  tests  of  the  same  apparatus  will  bring  iden- 
tical results.  Unless  the  speed  of  flow  is  accu- 
rately gauged,  the  results  will  differ. 

The  temperature  test  is  sometimes  used  to  de- 
termine the  efficiency  of  these  holders.  When  this 
method  of  testing  is  employed  it  is  the  practice  to 
fill  the  holders  with  water  in  the  same  manner  as 
with  the  color  test.  The  temperature  of  the  water 
116 


FROM    THE    PRACTICAL    VIEWPOINT 

as  it  leaves  the  heater  is  then  suddenly  raised 
5°  to  10°,  and  the  time  at  which  the  rise  takes 
place  is  noted.  A  careful  watch  is  then  kept  at  the 
outlet  of  the  holder  to  determine  when  any  rise  in 
temperature  occurs  at  this  point.  The  elapsed  time 
indicates  the  time  of  holding.  The  temperature, 
instead  of  being  raised,  may  be  lowered  a  given 
amount  at  the  heater,  and  the  corresponding  drop 
in  temperature  at  the  outlet  noted. 

The  inaccuracy  of  this  method  of  testing  is  due 
to  the  fact  that  during  the  long  holding  period 
there  is  a  natural  tendency  for  the  changed  tem- 
perature to  become  diffused  throughout  the  sur- 
rounding liquid.  It  can  also  be  seen  that  when 
the  temperature  is  raised  the  natural  tendency  is 
for  the  hotter  liquid  to  remain  on  top  of  the  tank, 
while  if  the  temperature  is  dropped,  the  tendency 
is  for  the  cooler  liquid  to  settle  toward  the  bot- 
tom of  the  tank.  A  graphic  chart  can  be  made 
showing  the  result  of  these  tests  very  clearly. 
Using  the  upright  gradations  of  the  chart  to  indi- 
cate changes  in  temperature,  and  the  horizontal 
gradations  to  indicate  periods  of  time,  the  sudden 
rise  at  the  heater  will  be  clearly  shown  by  an  al- 
most perpendicular  line.  The  line  showing  the 

117 


THE    PASTEURIZATION    OF    MILK 

rise  of  temperture  at  the  outlet  will  be  compara- 
tively gradual  in  its  rise  and  will  not  reach  its 
highest  point  for  a  considerable  time.  It  will  also 
be  found  that  the  proportional  rise  in  temperature 
at  the  outlet  will  not  be  as  great  as  at  the  inlet 
of  the  holder.  When  the  temperature  of  the  inlet 
is  dropped  instead  of  being  raised,  it  will  be  found 
that  the  change  of  temperature  at  the  outlet  occurs 
in  a  much  shorter  space  of  time. 

In  choosing  between  the  color  test  and  the  tem- 
perature test,  it  can  safely  be  said  that  for  the 
Park  holder  the  color  test  is  the  more  accurate. 
When  the  tubular  holder  is  used,  which  will  be  de- 
scribed later,  it  is  probable  that  the  two  tests  are 
nearly  equal  in  accuracy. 

When  two  or  more  tanks  are  employed  in  series, 
it  is  desirable  that  the  piping  be  so  arranged  that 
the  lowest  tank  can  be  filled  with  milk  first  when 
the  process  of  pasteurizing  is  commenced  for  the 
day,  and  then  when  the  lower  tank  is  full  the  up- 
per tanks  should  be  filled  and  the  process  contin- 
ued in  this  manner.  The  milk  will  then  flow 
through  all  the  tanks  in  succession  from  the  high- 
est to  the  lowest.  The  reason  for  filling  the  lower 
tank  first  is  as  follows:  When  each  tank  is  first 
118 


FROM    THE    PRACTICAL    VIEWPOINT 

filled,  the  milk  of  course  falls  from  the  inlet  pipe 
at  the  top  to  the  bottom  of  the  tank,  and  afterward 
onto  the  surface  of  the  body  of  milk  in  the  tank  as 
it  fills  up  to  the  level  of  the  outlet  pipe.  In  conse- 
quence there  is  considerable  agitation  of  the  liquid 
and  currents  are  created.  This  may  cause  the  last 
milk  which  enters  the  tank  to  be  the  first  to  be 
discharged,  and  our  holding  time  becomes  a  mat- 
ter of  uncertainty.  If,  however,  the  lower  tank  is 
the  first  one  filled,  we  are  then  sure  that  all  the 
milk  in  this  tank  is  held  for  at  least  the  time  re- 
quired for  the  other  tanks  to  fill. 

This  method  of  filling  may  be  effected  in  either 
of  two  ways:  First,  a  pipe  may  extend  along  the 
top  of  the  tanks  in  such  a  way  that  by  opening  the 
proper  valves  the  milk  may  be  directed  into  either 
tank  at  will.  Second,  the  pipe  may  be  arranged 
at  the  bottom  of  the  series  in  such  a  way  that 
either  tank  may  be  filled,  if  the  proper  valves  are 
opened  and  closed.  Both  arrangements  of  pipes 
are  shown  in  Fig.  24. 

It  has  been   found  by  tests   that  this   form   of 

holder  never  holds  the  milk  for  a  period  of  time 

as  long  as  that  which  is  required  for  them  to  be 

filled.     Depending  upon  the  form  of  the  tanks  and 

119 


THE    PASTEURIZATION    OF    MILK 

the  method  of  construction,  the  percentage  of  hold- 
ing time  to  filling  time  is  from  25  per  cent,  to  70 
per  cent.  It  is  usual  to  estimate  the  time  as  60  per 
cent,  of  the  filling  time.  It  is  true  that  tanks  which 
are  tall  and  of  comparatively  narrow  diameter  are 
more  efficient  than  are  short  and  wide  tanks,  the 
reason  probably  being  that  with  long,  narrow  tanks 
the  movement  of  milk  is  comparatively  rapid,  and 
there  is  less  diffusion  of  the  milk  than  when  the 
movement  is  slow,  as  in  the  wide,  short  tank.  Tests 
have  been  made  which  indicate  that  when  the  rate 
of  flow  is  twelve  feet  or  over  a  minute,  there  is 
very  little  diffusion  of  the  liquid. 

In  all  tanks  of  this  character  it  is  desirable,  and 
indeed  almost  a  necessity,  that  some  sort  of  an 
insulating  jacket  be  provided  in  order  that  there 
be  as  little  loss  of  temperature  as  possible  during 
the  holding  process.  The  reason  for  this,  as  be- 
fore stated,  is  that  the  cooling  of  the  milk  which 
is  near  the  outer  circumference  of  the  tank  causes 
downward  currents.  Thus  the  milk  which  falls 
to  the  bottom  on  account  of  these  currents  is  car- 
ried out  of  the  tank  before  it  has  been  held  for  the 
proper  length  of  time. 

The  insulation  may  be  provided  by  means  of 
120 


FROM    THE    PRACTICAL    VIEWPOINT 

jackets  of  asbestos,  cork  or  felt,  or  a  surround- 
ing tank  of  water  may  be  provided,  as  in  Fig.  25. 
By  means  of  the  insulation,  if  properly  applied, 
the  heat  will  be  retained  and  the  milk  as  it  flows 
from  the  tank  will  have  a  temperature  but  little 
below  that  at  which  it  enters.  When  the  hot  water 
insulation  is  used,  as  in  Fig.  25,  the  initial  tem- 
perature of  the  milk  may  become  somewhat  in- 
creased during  the  holding  period.  This  addi- 
tional heating,  it  can  be  seen,  has  a  tendency 
to  cause  the  milk  which  may  enter  the  tank  below 
the  average  temperature  to  become  heated  and  rise 
toward  the  top  of  the  tank,  thus  increasing  the 
time  for  which  it  is  held.  As  a  matter  of  fact,  the 
water-insulated  tanks  have  shown  a  good  percent- 
age of  holding  time  as  compared  with  the  filling 
time  when  the  color  test  has  been  applied.  The 
test  of  their  efficiency  as  measured  by  the  destruc- 
tion of  the  bacteria  contained  in  the  milk  is  also 
good. 

This  Park  type  of  holding  tank  has  been  some- 
what modified  by  various  manufacturers  in  this  re- 
spect, namely,  by  introducing  the  milk  at  the  bot- 
tom and  allowing  it  to  flow  out  at  the  top  instead 
by  the  reverse  method  of  flow.  When  the  inlet 
121 


THE    PASTEURIZATION    OF    MILK 

pipe  from  the  heater  enters  the  tank  at  the  centre 
of  the  bottom,  and  the  milk  is  forced  upward  till 
the  tank  is  filled,  the  color  tests  made  have  indi- 
cated that  their  efficiency  percentage  was  small. 
Especially  was  this  true  when  the  outlet  pipe  was 
at  one  side  and  near  the  top  of  the  tank.  It  can 
be  seen  that  the  force  which  is  necessary  to  impel 
the  milk  in  at  the  bottom  against  the  weight  of 
the  superimposed  milk  in  the  tanks  must  of  neces- 
sity create  currents.  This  will  be  more  noticeable 
if  the  milk  is  forced  through  the  heater  by  means 
of  a  pump.  The  impulses  will  create  a  somewhat 
uneven  flow  and  the  resulting  currents  will  be 
greater.  The  discharge  of  the  milk  from  one  side 
of  the  top  also  tends  to  cause  currents  and  an 
uneven  overflow. 

One  manufacturer  has  so  constructed  his  tanks 
that  the  inlet  pipe  enters  at  the  top  through  the 
cover,  is  carried  down  through  the  body  of  the 
milk  in  the  tank  to  the  bottom,  and  then  dis- 
charges the  milk  into  the  tank  by  means  of  an 
enlarged  perforated  foot  somewhat  resembling  a 
sprinkler  head  on  a  watering  can.  In  the  plants 
where  this  apparatus  is  used  the  milk  flows  by  grav- 
ity and  there  are  thus  no  pump  impulses.  The 
122 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  25 


force  is  broken  up  by  the  descent  of  the  milk 
through  the  body  of  that  in  the  tank.  It  can  be 
seen  that  when  the  milk  as  it  enters  the  tank  is  be- 
low the  average  temperature,  the  tendency  will  be 
123 


THE    PASTEURIZATION    OF    MILK 

for  it  to  remain  at  the  bottom,  and  so  be  heated 
before  it  is  discharged.  In  this  holder,  also,  the 
outflow  is  from  the  top,  but  the  flowage  into  the 
discharge  pipe  is  from  many  points  at  the  surface 
into  a  gathering  pan.  In  this  way  surface  cur- 
rents are  avoided. 

One  of  the  disadvantages  of  the  upright  tank 
holder  is  that  when  it  is  of  large  size  it  is  rather 
difficult  to  clean.  It  becomes  necessary  for  the 
workmen  to  get  inside  the  tank  in  order  to  thor- 
oughly clean  it.  Some  upright  tanks  are  being 
made  which  are  mounted  upon  trunions  in  such  a 
way  that  when  the  pipes  are  disconnected  the  tank 
may  be  turned  into  a  horizontal  position,  and  the 
cleaning  can  then  be  more  easily  performed. 

A  second  form  of  continuous  or  flow  type  tank 
is  so  constructed  that  a  long  horizontal  tank,  which 
opens  at  the  top,  is  divided  by  cross  partitions  into 
several  compartments.  At  the  top  of  each  of  these 
partitions  is  a  gathering  trough,  extending  along 
the  upper  edge  of  the  partition.  A  tube  attached 
to  the  centre  of  this  trough  extends  to  near  the 
bottom  of  the  next  succeeding  compartment.  This 
is  shown  in  Fig.  26. 

In  operation,  the  milk  enters  into  the  compart- 
124 


FROM    THE    PRACTICAL    VIEWPOINT 


FIG.  26 

ment  at  one  end  of  the  tank,  and  when  the  com- 
partment is  full,  the  milk  flows  into  the  gathering 
trough  and  is  carried  by  means  of  the  tube  to  the 
bottom  of  the  succeeding  compartment.  Here  the 
same  routine  is  repeated  till  all  the  compartments 
are  full.  Then  the  flow  becomes  continuous  till 
all  the  milk  is  pasteurized.  When  all  the  milk  has 
left  the  heater,  of  course  the  flow  from  the  holder 
stops.  The  tanks  are  at  this  time  all  full,  and 
it  is  then  necessary  to  remove  the  plug  which  is 
125 


THE    PASTEURIZATION    OF    MILK 

near  the  bottom  of  each  compartment  in  turn 
till  all  are  emptied.  Since  these  plugs  are  re- 
moved by  hand,  it  is  necessary  to  place  the  hand 
and  arm  into  the  empty  compartment  at  each 
operation.  The  danger  of  contamination  is  thus 
evident. 

When  the  partitions  are  low  it  has  been  found 
that  the  milk  flows  over  the  tops  of  all  of  them, 
and  there  is  thus  but  little  holding  time  possible, 
since  the  milk  flows  almost  directly  from  the  inlet 
to  the  outlet  pipe.  Even  with  the  best  of  con- 
struction, tests  have  shown  that  the  percentage  of 
holding  time  to  the  filling  time  is  small,  sometimes 
being  as  low  as  10  per  cent,  to  15  per  cent. 

The  third  form  of  continuous  flow  type  holder 
now  used  quite  extensively  is  shown  in  Fig.  27.  It 
consists  of  a  series  of  large-size  tubes  arranged  in 
a  box- like  structure.  These  tubes  are  connected 
one  with  another  at  the  ends  by  suitable  hinged 
heads,  so  that  the  milk  which  enters  the  top  tube 
of  the  series  flows  forward  and  backward  through 
all  of  them  and  is  discharged  from  the  lower  tube. 
The  discharge  pipe  is  carried  upward  in  the  form 
of  an  inverted  U  tube  in  a  similar  manner  to  that 
shown  in  Fig.  24.  This  gives  assurance  that  no 
126 


FROM    THE    PRACTICAL    VIEWPOINT 


127 


THE    PASTEURIZATION    OF    MILK 

milk  will  be  discharged  until  all  the  tubes  have 
become  filled. 

In  this  form  of  holder,  the  flow  of  milk  through 
the  apparatus  is  comparatively  rapid.  As  before 
stated,  this  rapid  flow  tends  to  prevent  diffusion, 
and  the  holding  time  more  nearly  approaches  the 
time  required  to  fill  the  apparatus  than  in  any 
other  form  of  flow-type  holder.  In  some  respects 
it  is  rather  difficult  to  make  a  satisfactory  color 
test  upon  this  holder  on  account  of  the  fact  that 
the  air,  which  of  course  fills  the  holder  when  the 
filling  with  milk  is  commenced,  is  not  all  forced 
out  as  completely  as  is  desired,  and  thus  air  pock- 
ets are  formed.  It  thus  occurs  that  some  milk  is 
forced  from  the  discharge  tube  before  the  appara- 
tus is  completely  filled.  Thus  it  is  difficult  to  ob- 
tain the  exact  time  required  to  fill  the  tubes.  It 
is  claimed  by  the  manufacturers  that  when  it  is 
operating  under  the  most  favorable  conditions  the 
milk  will  be  held  for  98  per  cent,  of  the  time  re- 
quired for  the  apparatus  to  become  filled.  The 
tests  observed  by  the  writer  indicate  that  the  hold- 
ing time  is  from  80  per  cent,  to  90  per  cent,  of  the 
filling  time,  which  is  a  greater  percentage  than 
with  other  holders. 

128 


FROM    THE    PRACTICAL    VIEWPOINT 

The  same  difficulty  which  is  experienced  in 
emptying  the  tubular  heater  is  observed  with  rela- 
tion to  the  tubular  holder.  This  is  due  to  the  very 
slight  inclination  or  pitch  of  the  tubes  from  the 
horizontal.  In  some  cases  it  has  been  the  prac- 
tice to  force  the  last  milk  out  of  the  tubes  by  fol- 
lowing it  with  water.  The  possibility  of  adul- 
terating the  milk  unless  great  care  is  exercised  is 
apparent.  In  the  later  machines  made,  the  tubes 
are  given  a  greater  pitch,  and  the  objection  due  to 
slow  drainage  is  at  least  reduced. 

It  should  be  noted  that  unless  the  tubes  are  very 
thoroughly  heated  by  means  of  hot  water  or  steam 
immediately  before  use,  the  first  milk  entering  the 
holder  will  be  so  cooled  that  its  temperature  at  the 
discharge  will  be  below  that  which  is  required. 

This  form  of  holder  can  be  easily  cleaned,  since 
the  tubes  are  large,  and  can  be  readily  opened. 
It  is  thus  easy  to  force  a  suitable  brush  through 
the  pipes,  and  it  is  not  difficult  to  see  if  all  dirt 
has  been  removed.  It  is  of  course  necessary  that 
the  cleaning  be  performed  with  great  thorough- 
ness in  order  that  it  be  effective  in  the  destruction 
of  bacteria. 

Whatever  form  of  holder  is  used,  whether  it  be 
129 


THE    PASTEURIZATION    OF    MILK 

of  the  absolute  or  the  continuous  type,  careful 
sterilization  should  be  practised,  not  only  directly 
after  the  apparatus  is  washed  each  day,  but  also 
immediately  before  its  use  on  the  following  day. 
The  reason  for  this  is  due  to  the  fact  that  any 
organic  matter  which  may  remain  in  the  apparatus 
after  washing  may  contain  spores  of  bacteria 
which  are  not  readily  killed  by  the  heating  to 
which  the  apparatus  is  usually  subjected.  These 
spores  may  develop  into  active  bacteria  during  the 
time  that  the  apparatus  remains  idle.  Especially 
would  this  be  true  if,  as  usually  occurs,  consid- 
erable moisture  is  allowed  to  remain  in  the  machine. 
For  this  reason  the  holder  should  be  thoroughly 
sterilized  before  use  each  day.  It  may  here  be 
noted  that  there  is  even  a  greater  necessity  for 
sterilizing  the  cooler,  pipes,  bottling  machine,  etc., 
with  which  the  pasteurized  milk  comes  in  contact 
after  leaving  the  holder.  Any  recontamination  at 
these  points  is  not  afterward  corrected  and  may 
be  a  source  of  danger. 

It  should  here  be  noted  that   a   feature   which 
has   been   introduced   into   some   milk   plants   con- 
sists in  a  brief  superheating  of  the  milk  after  it 
leaves  the  holder.     This  is  accomplished  by  allow- 
130 


FROM    THE    PRACTICAL    VIEWPOINT 

ing  the  milk  to  flow  in  a  thin  layer  over  pipes 
which  are  heated  to  about  162°  to  165°.  The  milk 
is  then  immediately  cooled.  It  is  claimed  that  bac- 
teria which  are  resistant  to  142°  temperature  are 
nevertheless  considerably  weakened  by  this  heat- 
ing,, and  are  completely  destroyed  at  the  brief 
heating  of  162°.  It  is  also  claimed  that  the  cream 
rises  in  a  more  satisfactory  manner  when  the  ad- 
ditional heating  is  employed.  The  feature  of  ap- 
plying a  brief  superheating  temperature  to  milk 
already  pasteurized  has  been  covered  by  a  patent. 

It  must  be  evident,  when  a  little  thought  is 
given  to  the  matter,  that  in  order  for  any  con- 
tinuous holder  to  be  reliable,  the  rate  of  milk  flow 
must  be  uniform.  In  very  few  forms  of  appara- 
tus is  there  any  attempt  to  properly  control  the 
rate  of  flow.  When  milk  flows  by  gravity,  the 
rate  at  which  it  flows  into  the  heater  will  depend 
partly  upon  the  volume  of  the  fluid  in  the  tank 
which  feeds  the  machine.  WThen  a  pump  is  used 
to  supply  the  heater,  its  rate  of  delivery  may  be 
influenced  by  the  steam  pressure,  or  by  the  degree 
to  which  the  steam  valve  is  opened,  or  by  the  con- 
dition of  the  valves  and  pistons.  In  places  where 
a  gravity  flow  is  employed,  it  is  not  a  difficult  mat- 
131 


THE    PASTEURIZATION    OF    MILK 

ter  to  arrange  a  feed  cup  which  will  make  it  cer- 
tain that  no  more  than  a  definite  amount  of  milk 
can  reach  the  heater  per  hour.  When  a  pump  is 
used,  a  float  valve  in  the  tank  which  feeds  the 
heater  can  be  made  to  shut  off  the  intake  pipe  to 
the  feed  tank.  This  increases  the  milk  pressure 
upon  the  pump  and  the  discharge  pipe,  and  by 
means  of  a  suitable  valve  this  increased  pressure 
is  made  to  close  the  steam  valve  which  supplies  the 
pump.  This  method  of  controlling  the  flow  of 
milk  to  the  heater  is  in  successful  operation  in 
several  pasteurizing  plants. 


132 


CHAPTER    IV 

TEMPERATURE     CONTROLLERS     AND    RECORDERS 

In  order  that  uniformly  good  results  in  the  pas- 
teurization of  milk  may  be  obtained,  it  is  abso- 
lutely necessary  that  the  temperature  to  which  the 
milk  is  heated  be  controlled  in  such  a  way  that 
there  will  be  no  great  variation.  In  order  to  con- 
trol this  properly,  three  things  are  necessary — 
first,  a  uniform,  even  flow  of  milk;  second,  a  steam 
pressure  which  does  not  vary;  and  third,  that  the 
steam  which  is  admitted  to  the  heater  be  so  con- 
trolled that  whatever  variations  there  may  be  in 
the  temperature  of  the  inflowing  cold  milk  may  be 
met  by  varying  amounts  of  steam,  admitted  to  the 
heater.  This  control  will,  of  course,  also  prevent 
any  excessive  heating  which  would  follow  if  too 
much  steam  entered  the  heating  apparatus. 

The  matter  of  an  even  milk  flow  has  been  dis- 
cussed in  the  previous  chapter. 

The  control  of  steam  pressure  may  be  accom- 
plished in  various  ways.  It  is,  of  course,  necessary 
that  there  be  sufficient  boiler  capacity  to  insure 
that  the  steam  pressure  does  not  fall  below  a  cer- 
133 


THE    PASTEURIZATION    OF    MILK 

tain  minimum  amount.  One  of  the  simplest  meth- 
ods of  steam  pressure  control  is  by  an  instrument 
constructed  like  the  safety  valve  of  a  boiler.  A 
movable  weight  upon  an  arm  regulates  the  pressure 
which  is  desired.  When  properly  set  any  increase 
of  pressure  above  the  desired  amount  lifts  the  arm 
and  shuts  the  steam  valve  connecting  with  the  pipe 
leading  to  the  heater.  Other  more  complicated 
forms  of  apparatus  are  on  the  market,  the  details 
of  which  it  is  not  necessary  to  describe. 

In  the  matter  of  the  control  of  the  temperature 
at  which  the  milk  leaves  the  heater,  it  is,  of  course, 
possible  to  do  this  by  hand.  This  method  makes  it 
necessary  that  a  man  constantly  watch  the  ther- 
mometer attached  to  the  outlet  milk  pipe,  and  at 
the  same  time  open  or  close  the  steam  valve  to  ad- 
just the  steam  flow  to  the  varying  temperature  of 
the  milk. 

If  the  speed  of  milk  flow,  and  also  the  steam 
pressure  is  well  controlled,  it  is  possible  for  a  care- 
ful workman  to  regulate  the  milk  temperature  with 
good  success.  If,  however,  these  factors  are  con- 
stantly varying,  it  is  nearly  impossible  for  even  a 
careful  man  to  obtain  good  results.  It  is,  of  course, 
more  economically  efficient  to  arrange  for  auto- 
134 


FROM    THE    PRACTICAL    VIEWPOINT 

matic  temperature  control  than  to  depend  upon 
man  power,  provided,  of  course,  that  the  machine 
works  as  it  is  intended  to  work. 

The  machines  designed  to  control  temperatures 
are  operated  in  two  ways.  In  one  machine  the 
bulb  which  is  inserted  into  the  milk  is  filled  with 
some  volatile  liquid  like  ether  and  is  connected 
by  means  of  a  capillary  tube  with  a  pressure  coil, 
which  in  turn  regulates  the  flow  of  compressed  air 
to  a  valve.  The  compressed  air  is  employed  as  a 
motive  power  to  operate  the  valve  which  regulates 
the  admission  of  steam  to  the  milk  heater.  Such  a 
system  involves  the  installation  of  an  air  pump 
and  a  tank  for  the  storage  of  compressed  air.  To 
one  unfamiliar  with  the  apparatus  the  description 
may  appear  involved  and  the  operation  compli- 
cated. Fig.  28  shows  this  system. 

In  another  form  of  controller,  electricity  is  em- 
ployed as  a  motive  power  in  operating  the  steam 
valve  instead  of  compressed  air.  The  bulb  which 
enters  the  milk  contains  two  metals,  which  are  so 
fastened  together  that  the  difference  in  expan- 
sion makes  and  breaks  the  electrical  connection 
and  the  steam  valve  is  operated  by  this  means. 
This  is  shown  in  Fig.  29-  This  method  can,  of 
135 


THE    PASTEURIZATION    OF    MILK 


FROM    THE    PRACTICAL    VIEWPOINT 


ELECTRICAL   CONJROLER 


SECTION  OF 
PASTEURIZER 


FIG.  29 


course,  be  employed  only  where  an  electric  current 
is  available.  This  current,  however,  may  be  fur- 
nished by  a  small  inexpensive  dynamo,  which  can 
be  operated  at  any  plant  where  power  is  available. 
Both  these  forms  of  control  work  in  a  satisfactory 
manner.  Of  course,  they  are  somewhat  delicate 

137 


THE    PASTEURIZATION    OF    MILK 

in  adjustment,  and  careful  handling  is  necessary. 
Either  form  will  control  the  milk  temperature 
within  2°,  as  indicated  by  the  temperature  re- 
corder. 

A  method  of  temperature  control  which  was 
proposed  by  the  writer  some  years  ago  had  for  its 
basis  a  principle  which  has  been  made  use  of 
in  this  connection  to  a  limited  extent  only.  This 
consisted  in  this,  namely,  that  the  temperature  of 
the  heating  medium  be  so  controlled  as  to  remain 
constant,  and  that  the  milk  which  flowed  out  of 
the  heater  be  kept  at  a  uniform  temperature  by 
varying  the  speed  of  flow  of  the  milk  through 
the  heater.  This  reverses  or  inverts  the  present 
practice,  in  which  the  speed  of  milk  flow  is  con- 
stant, while  the  temperature  of  the  heating  med- 
ium varies.  The  proposed  method  would  have 
this  advantage,  that  no  part  of  the  milk  could  ever 
be  heated  higher  than  the  temperature  of  the  water, 
and  if  this  water  temperature  were  controlled  by 
a  thermostat  no  scorching  of  the  milk  would  ever 
result.  It  is  evident  that  with  a  uniform  heating 
medium  the  milk  which  flows  through  the  heater 
will  take  up  more  of  this  heat  if  the  speed  of  flow 
is  slow  than  it  will  if  the  milk  moves  rapidly  over 
138 


FROM    THE    PRACTICAL    VIEWPOINT 

the  heating  surface.  A  thermostat  attached  to  the 
milk  outlet  pipe  from  the  heater  could  be  made 
to  control  the  steam  which  supplied  the  milk 
pump.  This  would  vary  the  speed  of  milk  flow. 
If  milk  flows  by  gravity  to  the  heater,  the  ther- 
mostat might  be  made  to  open  or  close  a  valve  in 
the  feed  pipe. 

The  nearest  approach  to  the  use  of  this  prin- 
ciple occurs  in  some  plants  when  the  heated  water 
is  kept  at  a  uniform  temperature  by  a  thermostat, 
and  the  milk  flow  is  also  constant.  The  heating 
surface  of  the  heater  is  so  very  large  compared  to 
the  amount  of  milk  heated,  that  the  water  is  never 
more  than  3°  or  4°  hotter  than  the  milk,  and 
there  is  therefore  no  possibility  of  scorching  the 
milk.  In  these  plants  also  the  efficiency  of  the  re- 
generative principle  is  carried  as  near  the  theo- 
retical limit  of  perfection  as  it  seems  possible.  The 
water  leaving  the  heater  is  within  a  few  degrees  of 
the  temperature  of  the  cold  milk  entering  the  ma- 
chine. This  cooled  water  is  conveyed  to  the  milk 
cooler,  where  it  is  used  for  cooling  the  hot  milk. 
It  becomes  so  heated  when  leaving  the  cooler  that 
it  is  but  a  few  degrees  lower  than  the  hot  milk. 
It  can  be  seen  that  but  little  steam  is  required  to 
139 


THE    PASTEURIZATION    OF    MILK 

again  raise  the  temperature  to  the  desired  point. 
The  increased  amount  of  heating  and  cooling  sur- 
faces required  for  this  form  of  pasteurizing  ma- 
chine calls  for  careful  cleaning  and  sterilization. 

Automatic  Recorders 

The  automatic  recording  of  the  milk  temperature 
is  desirable,  and  in  most  cities  where  the  pas- 
teurization of  milk  is  subject  to  public  control  it 
is  required.  The  milk  company  which  is  really 
anxious  to  put  out  a  safe  product  wants  an  office 
record  which  will  indicate  whether  the  work  is 
being  properly  performed.  With  health  authori- 
ties, such  a  record  is  necessary,  since  it  is  impos- 
sible for  inspectors  to  be  at  pasteurizing  plants  all 
of  the  time  to  watch  their  operations.  A  correct 
automatically  made  record  is  the  best  substitute 
for  personal  inspection.  To  be  of  ideal  value,  such 
a  record  should  show,  not  only  the  temperature,  but 
also  the  time  of  holding.  When  the  tank  or  batch 
heater  is  used,  the  single  recorder  attached  to  the 
tank  will  show  these  items  with  fair  accuracy,  but 
the  observer  must  note  whether  or  not  the  cooling 
is  either  wholly  or  partially  done  in  the  tank  itself. 
140 


FROM    THE    PRACTICAL   VIEWPOINT 

If  such  cooling  in  the  tank  does  take  place,  then 
the  length  of  time  for  which  the  recording  mark 
remains  at  the  highest  point  is  a  correct  indica- 
tion of  the  time  for  which  the  hot  milk  is  held. 
If  the  cooling  is  performed  entirely  outside  the 
holding  tank,  then  allowance  must  be  made  for  the 
time  necessary  for  the  milk  as  drawn  from  the 
tank  to  fall  below  the  point  where  the  thermome- 
ter bulb  is  inserted  into  the  milk.  It  is  plain  that 
the  making  of  the  record  by  the  recorder  pen  will 
continue  as  long  as  the  bulb  remains  in  the  hot 
milk.  Thus,  if  the  highest  temperature  were  re- 
corded for  forty-five  minutes,  and  it  required  twen- 
ty-five minutes  for  the  milk  in  its  discharge  to  fall 
below  the  recorder  bulb,  then  the  actual  holding 
time  for  all  of  the  milk  would  be  but  twenty 
minutes. 

When  the  continuous  holding  process  is  used,  it 
is  desirable  that  a  recorder  be  attached  to  the  out- 
let of  the  heater,  and  that  another  be  placed  in  the 
outlet  pipe  from  the  holder.  If  the  charts  on  these 
two  recorders  are  both  set  at  the  correct  hour  of 
the  day  then  it  is  easy  to  calculate  the  duration 
between  the  time  of  the  first  discharge  of  hot  milk 
from  the  heater  and  the  first  discharge  from  the 
141 


THE    PASTEURIZATION    OF    MILK 

holder.  If  one  recorder  only  is  in  use,  it  is  more 
important  that  it  be  placed  at  the  holder  outlet. 
It  is  evident  that  if  there  is  a  serious  loss  of  heat 
during  the  holding  process  due  either  to  imper- 
fect insulation  or  to  insufficient  preliminary  heating 
of  the  holder,  then  the  milk  would  not  be  satisfac- 
torily pasteurized,  since  some  of  the  dangerous 
organisms  originally  in  the  milk  may  escape  de- 
struction. The  holder  recorder  indicates  this. 

The  various  recording  instruments  upon  the 
market  differ  in  this  one  particular,  namely,  that 
in  one  form  ether,  or  a  similar  volatile  fluid,  is 
used  in  the  thermometer  bulb  and  capillary  tube, 
while  in  the  other,  the  bulb  and  tube  are  filled  with 
mercury.  One  of  the  former  is  shown  in  Fig.  30, 
while  the  mercury  bulb  is  shown  in  Fig.  31.  There 
is  a  variation  also  in  the  method  employed  for 
regulating  the  recording  arm.  In  a  form  of  re- 
corder not  shown,  another  form  of  adjusting  screw 
is  attached  to  the  recording  arm,  and  an  improved 
device  is  used  for  securing  the  paper  chart  to  the 
face  of  the  instrument. 

In  the  selection  of  a  recording  instrument,  one 
of  the  most  important  points  to  consider  is  its  sen- 
sitiveness to  rapid  or  frequent  changes  in  tempera- 
142 


FROM    THE    PRACTICAL    VIEWPOINT 


fi 


ill 


<QQ  -  o 


143 


THE    PASTEURIZATION    OF    MILK 


FIG.  31 

ture.  If  it  is  slow  in  responding  to  such  changes, 
there  is  a  possibility  that  there  may  be  a  wide 
fluctuation  of  temperature,  which  will  not  be  shown 
upon  the  recording  chart.  The  manufacturer  of 
each  instrument  claims  that  his  machine  is  very 
sensitive  to  rapid  temperature  changes. 

It  should  be  borne  in  mind  that  a  temperature 
144 


FROM    THE    PRACTICAL   VIEWPOINT 

recorder  is  in  reality  a  pressure  recorder  only  in 
which  the  changes  in  pressure  due  to  varying  tem- 
peratures are  so  graduated  as  to  indicate  with 
fair  accuracy  the  temperature  of  the  milk.  With 
the  ether  instrument,  the  amount  of  movement  of 
the  arm  for,  say,  a  ten  degree  rise,  changes  as  the 
higher  temperatures  are  reached.  So  the  grad- 
uations on  the  chart  are  not  of  the  same  width  all 
the  way  across.  In  the  mercury  instruments  this 
is  not  true,  but  the  degree  graduation  lines  are 
equally  distant  one  from  the  other.  There  are  cer- 
tain inaccuracies  in  these  instruments  which  must 
be  taken  into  account.  Thus  it  can  be  seen  that 
the  temperature  of  the  room  in  which  the  recorder 
is  placed  must  have  an  effect  upon  the  pressure 
coil.  In  the  instrument  shown  in  Fig.  30  an  at- 
tempt is  made  to  correct  this  by  attaching  to  the 
arm  a  compensating  coil.  This  coil  also  contains 
mercury,  and  is  so  placed  that  it  moves  in  a  di- 
rection opposite  to  that  of  the  coil  to  which  the 
capillary  tube  is  connected.  The  recording  arm 
is  attached  to  both  coils.  When,  therefore,  both 
coils  move  as  the  result  of  the  room  temperature, 
no  effect  is  produced  upon  the  recording  arm,  but 
it  remains  stationary.  Any  increased  pressure  in 
145 


THE    PASTEURIZATION    OF    MILK 

one  due  to  the  temperature  of  the  heated  milk  will 
move  the  pen  and  cause  it  to  make  a  proper  rec- 
ord. The  same  effect  may  be  produced  in  another 
way.  In  this  case  the  compensating  coil  is  con- 
structed of  two  different  metals,  and  the  differences 
in  expansion  cause  it  to  move,  but  in  a  direction 
opposite  to  that  produced  by  the  ether  coil. 

It  must  also  be  borne  in  mind  that  the  recorder 
does  not  register  absolute  temperatures,  but  only 
relative  changes  in  temperature.  Thus  inaccurate 
adjustment  of  the  arm  may  produce  a  record  which 
is  deceptive.  For  this  reason  it  is  necessary  to 
provide  some  means  of  adjusting  the  arm  in  order 
to  secure  an  accurate  reading.  In  some  instru- 
ments the  arm  has  a  flexible  joint  which  can  be 
moved  by  hand.  This  is  rather  difficult  to  accom- 
plish, without  danger  of  breaking  the  recording 
arm,  and  fine  adjustment  is  not  easy.  There  is 
also  the  danger  that  the  joint  will  be  uninten- 
tionally moved  when  placing  the  chart  upon  the 
face  of  the  dial. 

In  one  recorder  a  post  is  so  placed  that  it  can 

be  turned  by  means  of  a  clock  key.     After  the 

proper  adjustment  has  been  made,  the  post  may  be 

held  in  proper  position  by  sealing  it  to  other  rigid 

146 


FROM    THE    PRACTICAL    VIEWPOINT 

posts  beside  it.  This  form  is  of  value  to  the  in- 
spector, since  by  placing  his  seal  upon  it  he  can 
be  sure  that  no  change  is  made  in  the  recorder 
during  his  absence. 

In  other  instruments  other  means  of  adjustment 
are  provided.  If,  as  in  some  forms,  the  coil  is  so 
placed  that  its  axis  of  rotation  is  the  same  as  that 
of  the  recording  arm,  then  no  movement  of  the  arm 
at  the  joint  can  affect  the  relative  temperature 
valves  of  the  varying  degree  spaces  upon  the  chart. 
With  this  form  there  appears  also  to  be  less  lia- 
bility to  vibrate  with  the  vibration  of  the  walls  of 
the  buiding  in  which  it  is  placed.  This  form  also 
has  the  advantage  that  the  knob  or  screw  which 
holds  the  chart  to  the  face  of  the  dial  is  so  ar- 
ranged that  the  chart  cannot  be  left  loose  upon  the 
apparatus,  but  must  either  be  securely  fastened 
or  left  off  the  instrument  altogether.  It  is  also 
very  easy  to  fasten  the  chart  to  the  clock  face. 

It  has  frequently  been  found  by  inspectors  that 
instruments  were  not  accurately  adjusted.  This 
may  be  due  to  a  defect  in  the  instrument  itself,  or 
it  may  be  due  to  an  intentional  false  adjustment 
by  the  man  who  is  operating  the  pasteurizer.  He 
may  wish  to  indicate  upon  the  chart  a  higher  tem- 

147 


THE    PASTEURIZATION    OF    MILK 

perature  than  is  actually  employed  in  the  pas- 
teurization of  the  milk.  For  this  reason  those  in- 
struments whose  adjustment  is  under  the  control 
of  the  inspector  alone  are  desirable.  They  should 
be  frequently  tested.  This  frequent  checking  is  of 
advantage  to  the  honest  milk  dealer  as  well,  since 
if  a  recorder  by  any  means  shows  a  temperature 
lower  than  it  should,  there  may  be  trouble  with 
the  cream  line  due  to  an  unsuspected  high  tem- 
perature in  the  pasteurizer. 

Health  authorities  must  be  alert  in  watching  the 
temperature  records  which  are  kept  on  file  by  the 
dealer.  It  is,  of  course,  possible  for  a  dishonest 
dealer  to  make  false  records.  These  may  be  made 
in  various  ways.  Instances  have  been  known 
where  the  entire  record  has  been  made  by  hand, 
an  ordinary  pen  being  used.  This  requires  more 
skill  than  the  average  dealer  possesses,  if  he  is  to 
deceive  the  wideawake  inspector.  It  is  possible 
to  put  a  chart  upon  a  recorder  dial  and  leave  it  so 
loosely  attached  that  it  does  not  revolve  with  the 
clock.  Then,  when  the  desired  temperature  is 
reached,  the  chart  may  be  turned  by  hand  and  a 
beautiful  even  line  be  drawn  upon  it.  When  the 
first  milk  from  a  holder  has  a  temperature  lower 
148 


FROM    THE    PRACTICAL    VIEWPOINT 

than  required  by  law,  some  dealers  wait  until  the 
proper  temperature  is  attained,  and  then,  by  plac- 
ing the  thermometer  bulb  in  the  milk,  they  get  a 
record  which  indicates  an  immediate  rise  of  tem- 
perature to  the  highest  point,  and  then  a  uniformly 
even  line.  Any  record  which  indicates  that  the 
temperature  has  been  raised  at  once  to  the  maxi- 
mum point,  and  then  continues  with  no  variation 
during  the  entire  run,  should  be  looked  upon  with 
suspicion.  Inspectors  with  a  little  experience  soon 
learn  to  detect  false  records,  by  evidences  not  al- 
ways easy  to  explain,  and  they  are  able  to  gain 
from  dealers  the  admission  of  irregularities  which 
are  at  first  denied. 


149 


CHAPTER    V 

CLEANING     AND     COOLING     THE     MILK CLEANING 

CONTAINERS HOME     PASTEURIZATION,     ETC. 

It  is  of  course  needless  to  say  that  all  milk 
should  be  clean  when  it  arrives  at  the  plant  where 
it  is  to  be  pasteurized.  That  is,  there  should  be  no 
visible  dirt  in  the  milk.  It  is  also  desirable  that 
all  dirt  which  is  not  readily  detected  be  absent. 
While  visible  dirt  and  bacteria  are  not  identical, 
still  it  is  true  that  visible  dirt  is  almost  always  ac- 
companied by  bacteria  in  large  numbers.  Dealers 
should  therefore  make  every  effort  to  induce  the 
dairymen  to  be  so  cleanly  in  their  methods  that 
very  little  dirt  will  find  entrance  into  the  milk. 
The  sediment  test  when  properly  used  is  an  ex- 
cellent method  of  finding  out  whether  or  not  the 
dairyman  is  cleanly  in  his  methods.  If,  however, 
the  producer  is  allowed  to  strain  his  milk  before 
bringing  it  to  the  shipping  station,  then  the  sedi- 
ment test  simply  tells  the  dealer  whether  or  not 
the  farmer  has  strained  the  dirt  out.  Or  rather, 
let  us  say  it  indicates  either  that  the  farmers' 
methods  of  caring  for  the  milk  are  cleanly,  or  that 
150 


FROM    THE    PRACTICAL    VIEWPOINT 

the  evidence  of  his  uncleanliness  has  been  strained 
out.  It  seems  wise  to  advise  dealers  to  prohibit 
the  straining  of  milk  at  the  farm.  This  may 
seem  like  radical  doctrine,  but  a  little  thought  dis- 
closes its  wisdom.  If  the  milk  is  unstrained,  then 
the  sediment  test  becomes  of  real  value  to  the 
dealer  in  directing  his  attention  to  those  dairymen 
who  need  attention  from  the  inspector.  Then, 
again,  after  the  dirt  once  gains  access  to  the  milk, 
the  straining  simply  removes  that  part  of  the  dirt 
which  is  the  least  objectionable,  namely,  the  in- 
soluable  part.  If  milk  is  poured  over  a  strainer, 
the  dirt  remains  upon  the  surface,  and  the  milk 
which  may  be  afterward  poured  through  the 
strainer  helps  to  carry  through  those  soluble  por- 
tions which  may  have  at  first  escaped  solution. 
This  soluble  portion,  of  course,  contains  most  of 
the  bacteria. 

The  removal  of  the  dirt  at  the  shipping  sta- 
tion or  the  pasteurizing  plant  may  be  accom- 
plished by  straining  as  it  is  received,  or  since  the 
straining  of  cold  milk  is  difficult,  it  may  be  strained 
while  hot  from  the  heater  and  before  it  enters  the 
holding  apparatus.  There  is  no  objection  to  this, 
since  whatever  bacteria  are  carried  through  into 
151 


THE    PASTEURIZATION    OF    MILK 

the    holder    are    destroyed    during    the    holding 
process. 

Clarification 

The  centrifugal  clarifier  is  used  to  a  large  ex- 
tent, and  removes  not  only  the  dirt  which  is  ordi- 
narily seen  in  milk,  but  also  the  pus  cells,  blood 
cells,  etc.,  which  usually  escape  detection.  The 
clarifier,  as  is  well  known,  is  made  in  a  manner 
similar  to  a  separator,  the  difference  being  that 
the  cream  is  not  separated  from  the  milk,  but  the 
dirt,  pus,  etc.,  is  thrown  against  the  outer  por- 
tions of  the  revolving  shell,  and  is  there  collected. 
Of  course,  this  material  contains  a  great  many  bac- 
teria, which  are  carried  along  with  the  heavier  ma- 
terial. Tests,  however,  made  by  the  plating 
method,  do  not  show  the  great  decrease  in  the 
number  of  bacteria  which  might  be  expected,  and 
in  many  instances  the  apparent  number  is  in- 
creased. This  is  probably  due  to  the  fact  that  the 
clumps  of  bacteria  are  broken  up  and  so  produce 
more  colonies  upon  the  plate  than  results  when 
they  remain  bunched  together  in  the  original  milk. 
One  of  the  clarifiers  is  illustrated  in  Fig.  32. 

One  objection  to  the  clarifier  has  been  the 
152 


FROM    THE    PRACTICAL    VIEWPOINT 


THE    PASTEURIZATION    OF    MILK 

tendency  which  there  was  to  create  foam,  espe- 
cially if  the  milk  were  cold.  This  foaming  is  due, 
of  course,  to  the  entrance  of  air  into  the  milk  dur- 
ing the  process.  Milk  which  has  been  previously 
pumped  seems  more  likely  to  foam  than  when 
pumps  have  not  been  used.  Machines  are  now 
made  by  which  the  air  is  excluded,  and  no  foam, 
or  almost  none,  is  produced  when  they  are  oper- 
ated, even  when  the  milk  is  cold.  It  is  generally 
held  that  the  clarification  of  milk  by  a  centrifugal 
machine  is  a  good  thing.  It  is  claimed  that  the 
pus  cells,  leucocytes,  etc.,  which  are  in  the  milk, 
tend  to  form  a  covering  for  the  bacteria  contained 
in  the  milk,  to  such  an  extent  that  they  are  some- 
what protected  and  are  not  so  readily  destroyed 
by  heat.  It  is  claimed  that  the  removal  of  this 
covering  by  means  of  the  clarifier  therefore  assists 
in  the  complete  destruction  of  the  bacteria.  This 
claim  has  not  been  fully  demonstrated  to  the  knowl- 
edge of  the  writer. 

It  is  the  practice  of  some  dealers  to  strain  the 
pasteuried  milk  as  it  enters  the  bottling  machine. 
This  is  to  be  condemned  unless  the  strainer  is 
completely  covered  and  is  sterilized  at  the  same 
time  that  the  final  sterilizing  of  the  bottler  occurs. 
154 


FROM    THE    PRACTICAL    VIEWPOINT 

In  fact,  any  straining  after  the  milk  leaves  the 
holding  apparatus  is  undesirable,  and  seems  to  be 
useless  if  the  milk  has  been  well  cleaned  before 
pasteurizing. 

Coolers 

The  rapid  cooling  of  heated  milk  has  been  held 
to  be  an  important  factor  in  the  satisfactory  pas- 
teurizing of  milk.  It  was  claimed  that  the  sud- 
den chilling  had  a  destructive  effect  upon  the  bac- 
teria, which  had  been  already  weakened  by  the 
heating.  Investigations  made  by  Ayers  and  John- 
son, however,  seem  to  indicate  that  when  the  cool- 
ing is  accomplished,  during  a  period  of  two  hours, 
there  is  no  noticeable  increase  in  bacterial  growth. 

There  are  three  general  types  of  milk  coolers 
in  use: 

First:  The  open  cooler  or  aerator.  This  consists 
of  a  series  of  tubes,  made  usually  of  copper  and 
well  tinned.  These  tubes  are  arranged  one  above 
another,  and  are  so  connected  at  the  ends  that  cold 
water  or  brine  is  forced  through  the  entire  series. 
The  water  flow  is  into  the  lower  tubes  and  up- 
ward through  the  series,  so  that  the  coldest  water 
comes  in  contact  with  the  coldest  milk.  This  form 
155 


THE    PASTEURIZATION    OF    MILK 


FIG.  33 


of  cooler  is  shown  in  Fig.  33.  The  cooler  is  usu- 
ally arranged  in  sections.  Through  the  upper 
section  cold  water,  frequently  well  water,  flows, 
while  the  lower  section  contains  ice  water  or  brine. 
This  form  of  cooler  is  very  effective  in  rapidly 
156 


FROM    THE    PRACTICAL    VIEWPOINT 

cooling  the  milk  when  it  is  made  large  enough  to 
take  care  of  the  milk  which  is  to  be  treated.  They 
are  made  by  various  manufacturers  in  forms  which 
vary  somewhat  in  details.  Some  are  so  arranged  that 
the  regenerative  principle  is  made  use  of.  In  most 
of  these  the  hot  milk  from  the  holder  is  allowed 
to  flow  over  pipes  through  which  the  incoming 
cold  milk  flows.  This  is  a  means  of  saving  heat 
units,  but  such  coolers  are  rather  difficult  to  clean, 
and  there  is  a  danger  that  the  pressure  of  the  cold 
milk  on  the  inside  of  the  pipes  will  find  openings 
through  which  the  milk  will  be  forced  into  the  pas- 
teurized milk  on  the  outside.  The  contamination 
which  results  is  not  corrected  by  repasteurization. 
Some  one  may  say  that  the  same  danger  exists  when 
the  cooling  medium  on  the  inside  of  the  pipes  is 
water.  This  is  true,  but  it  must  be  remembered 
that  the  water  pipes  do  not  need  to  be  taken  apart 
for  cleaning,  while  the  milk  pipes  must  of  neces- 
sity be  opened  for  cleaning  daily,  and  the  danger 
from  loosened  joints  is  therefore  greater. 

Another  objection  which  has  been  urged  to  the 
use  of  the  open  cooler  is  that  the  milk  is  exposed 
to  the  air,  and  that  there  is  great  danger  from 
air  contamination.  This  is  true  when  the  air  is 

157 


THE    PASTEURIZATION    OF    MILK 

full  of  dust  or  foul  odors.  In  most  milk  plants, 
however,  the  air  is  so  moist  that  little  dust  is  flying 
about,  and  recent  investigations  by  Ruehle  and 
Kulp  *  of  milk  contamination  by  stable  air  indi- 
cate that  even  under  unfavorable  conditions  the  air 
contamination  is  not  as  serious  a  matter  as  we  have 
supposed.  Of  course,  milk  coolers  can  be  en- 
closed by  tightly  fitting  metal  covers,  or  they  may 
be  located  in  separate  rooms  or  compartments,  and 
so  be  protected  from  contact  with  air  which  is 
questionable.  If  a  separate  room  is  provided, 
suitable  ventilation  should  be  secured  for  carrying 
off  steam,  and  the  opening  for  the  admission  of  air 
should  be  so  protected  that  the  incoming  air  will 
be  filtered. 

Since  it  is  difficult  to  clean  and  sterilize  metal 
covers  for  coolers,  it  seems  more  desirable  that  the 
milk  be  protected  by  enclosure  in  separate  rooms. 

The  complete  sterilization  of  this  open  type  of 
cooler  is  a  rather  difficult  matter.  The  reason  for 
this  is  that  the  cooling  surface  cannot  be  subjected 
to  the  action  of  steam  under  pressure.  The  usual 
method  employed  is  to  direct  live  steam  from  a 


*Bul.  409.  N.  Y.  Agricul.  Exp.  Sta. 
158 


FROM    THE    PRACTICAL    VIEWPOINT 

hose  against  the  outer  surface  of  the  pipes,  after 
the  washing  has  been  completed.  It  is  well  known 
that  steam  when  relieved  of  its  pressure  rapidly 
cools,  and  a  person  can  hold  his  hand  a  short 
distance  from  an  open  steam  pipe  with  no  incon- 
venience. It  often  happens  that  not  all  the  parts 
of  the  cooler  receive  the  benefit  of  even  this  re- 
duced temperature.  The  tubes,  of  course,  must 
be  empty  of  the  water  usually  contained  in  them 
before  they  are  steamed. 

It  might  be  feasible  to  provide  covers  for  these 
coolers  which  would  be  sufficiently  tight  to  allow 
the  pressure  of  the  steam  to  be  retained  to  some 
extent  before  it  escaped  into  the  outer  air.  Some 
covers  are  now  made  which  are  fairly  tight. 

The  best  way  to  sterilize  this  form  of  cooler  is 
to  have  the  tubes  of  sufficient  strength  so  that 
steam  may  be  admitted  on  the  inside  under  pres- 
sure. In  such  case  the  sterilization  is  from  the 
inside.  If,  while  the  pipes  are  hot  from  the  en- 
closed steam,  water  is  allowed  to  trickle  over  the 
outside,  this  is  heated,  and  is  itself  converted  into 
steam,  which  helps  to  cleanse  the  pipes. 

Care  should  be  taken  to  be  assured  that  the 
steam  which  rises  from  the  milk  while  being  cooled 

159 


!    ' 


THE    PASTEURIZATION    OF    MILK 

does  not  become  condensed  upon  any  unclean  sur- 
face, such  as  the  ceiling  or  a  metal  covering  over 
the  cooler,  and  from  thence  fall  back  into  the  milk. 
If  this  occurs,  very  serious  contamination  may 
result. 

Open  pipe  coolers  should  not  be  made  very  long 
in  relation  to  their  height.  It  can  be  seen  that 
the  water  flowing  through  long  pipes  will  become 
warmed  on  the  inner  surface  of  the  tubes,  while 
the  central  more  rapidly  flowing  core  may  still  be 
cool.  More  effective  cooling  is  obtained  where  this 
milk  flow  is  broken  up  by  frequent  turns  as  the 
water  is  returned  from  one  pipe  to  another. 

Second:  The  cooling  may  be  accomplished  in 
the  same  apparatus  in  which  the  milk  is  heated 
and  held.  This  can  be  done  when  the  tank  sys- 
tem of  pasteurization  is  employed,  as  illustrated  in 
Figs.  12,  13,  14,  14-B,  15,  16.  When  cooling  is  so 
carried  on,  the  cold  water  or  brine  takes  the  place 
of  the  hot  water  in  the  pipes,  by  means  of  which 
the  heating  was  originally  done.  It  is  found  in 
practice  that  when  the  same  coil  is  used  for  the 
brine  as  well  as  for  the  hot  water,  there  is  dan- 
ger that  careless  workmen  may  allow  the  brine  and 
the  water  to  become  mixed.  There  is  therefore  a 
160 


FROM    THE    PRACTICAL    VIEWPOINT 

loss  of  brine.  Some  heating  tanks  are  now  made 
with  double  coils,  one  of  which  is  used  for  heating 
and  the  other  for  cooling.  If  the  cooling  is  done^x 
in  tank  pasteurizers  there  is  the  advantage  that 
the  milk  comes  in  contact  with  no  additional  metal 
surface  or  other  material  after  it  is  placed  in  the 
tank  till  it  is  drawn  into  the  final  containers. 

The  principal  objection  to  the  tank  cooling  is 
that  usually  a  long  time  is  required  to  reach  the 
desired  low  temperature.  As  stated  in  the  chap- 
ter on  heaters,  the  time  is  frequently  from  an  hour 
to  an  hour  and  a  half.  Large  coils  and  a  rapid 
circulation  of  brine  will  decrease  this  cooling  time 
greatly. 

In  country  plants  at  a  distance  from  the  point 
of  milk  consumption,  the  time  of  cooling  is  an  im- 
portant consideration  from  the  dealers'  point  of 
view,  since  the  time  between  the  receipt  of  the  milk 
from  the  farmer  and  the  departure  of  the  milk 
train  is  limited. 

The  change  in  temperature  from  the  high  heat 
necessary  to  pasteurize  the  milk  to  the  cold  re- 
quired for  rapid  cooling  produces  a  considerable 
strain  upon  the  pipes  of  the  coils,  and  the  joints 
are  apt  to  become  weakened. 

161 


THE    PASTEURIZATION    OF    MILK 

Third:  The  tubular  cooler  is  being  used  to  a 
considerable  extent.  In  this  form  of  cooler  the 
pipes  through  which  the  hot  milk  flow  are  en- 
closed by  other  pipes,  through  which  cold  water 
is  forced  in  a  direction  opposite  to  the  flow  of 
the  milk.  These  coolers  are  exactly  similar  to 
the  tubular  heaters  illustrated  in  Figs.  7,  10, 
and  11. 

This  form  of  cooler  is  effective  and  rapid;  it  has 
this  advantage,  that  sterilization  by  steam  under 
pressure  can  be  made  complete.  There  is  the  same 
difficulty  in  emptying  the  tubes  which  was  noted 
in  describing  the  tubular  heater  and  holder,  and 
whatever  advantage  there  may  be  in  exposing  milk 
to  the  air  in  order  to  get  rid  of  bad  odors,  etc.,  is 
absent  from  the  tubular  cooler. 

The  regenerative  principle  is  made  use  of  in  the 
tubular  heater  and  cooler,  as  already  described, 
and  there  is  little  danger  of  the  milk  becoming 
contaminated  by  leakage  of  the  water,  since  the 
joints  of  the  water  pipes  do  not  come  in  contact 
with  the  joints  of  the  milk  pipes. 

One  of  the  most  efficient  forms  of  apparatus  to 
use  from  the  point  of  view  of  economy  of  heat 
units  is  probably  that  shown  in  Fig.  11.  The 
162 


FROM    THE    PRACTICAL    VIEWPOINT 

great  amount  of  piping,  however,  renders  it  diffi- 
cult to  keep  clean. 

Washing  of  Containers 

It  is  of  course  important  that  containers  in 
which  pasteurized  milk  is  placed  shall  be  thor- 
oughly cleaned  and  sterilized.  There  can  be  little 
advantage  gained  in  the  proper  pasteurization  of 
milk  if  it  is  to  be  immediately  placed  in  contain- 
ers which  are  not  free  from  all  dangerous  bacteria. 
The  relative  importance  which  the  cleaning  of  cans 
and  bottles  has  in  the  bacterial  content  of  milk 
has  not  been  recognized  to  the  extent  which  it 
deserves. 

Cracks  and  open  seams,  especially  in  milk  cans, 
may  harbor  particles  of  milk  which  are  heavily  in- 
fected with  bacteria,  which  in  many  cases  are  of  a 
type  which  are  difficult  to  destroy  by  ordinary 
methods.  Especially  is  this  true  if  the  cans  or 
covers  contain  moisture,  since  this  aids  in  the  de- 
velopment of  the  bacterial  life. 

It  is  undoubtedly  true  that  the  methods  em- 
ployed in  washing  bottles  are  generally  much  more 
satisfactory  than  those  in  use  in  handling  the  cans 
and  covers.  Bottle-washing  machines  of  various 
163 


THE    PASTEURIZATION    OF    MILK 

makes  are  on  the  market  which  perform  excellent 
work.  Some  of  these  employ  revolving  brushes, 
which  are  automatically  forced  into  the  bottles,  in 
which  a  strong  washing  solution  has  been  placed. 
In  others,  the  cleaning  is  accomplished  by  inject- 
ing under  high  pressure  jets  of  washing  solution 
into  the  inverted  bottles.  This  type  of  machine  is 
that  which  is  in  the  most  general  use  at  the  pres- 
ent time. 

As  usually  constructed,  this  washing  apparatus 
is  a  long  machine,  in  which  are  placed  several 
tanks  for  containing  the  washing  and  rinsing 
fluids.  One  tank  contains  a  strong  washing  solu- 
tion, another  contains  water  for  the  first  rinsing, 
and  a  third  contains  clean  water  for  the  final  rinse. 
Over  these  tanks  are  placed  plates  having  a  sur- 
face area  of  about  the  same  size  as  that  of  the  top 
of  a  bottle  case.  These  plates  are  perforated,  and 
powerful  pumps  force  the  liquid  in  the  tanks 
through  these  perforated  plates  in  such  a  way  that 
the  liquid  is  forced  upward  into  the  bottles,  which 
are  inverted  in  cases  over  them.  An  automatic 
feed  pushes  the  cases  from  plate  to  plate  along  a 
track  made  for  the  purpose.  The  bottles  thus  get 
first  a  cleaning  with  the  fairly  hot  washing  solu- 


FROM    THE    PRACTICAL    VIEWPOINT 

tion,  then  a  rinsing  with  hot  water,  after  which 
clean  water  is  forced  into  them,  which  is  near  the 
boiling  temperature,  and  sometimes  a  final  jet  of 
live  steam  is  forced  into  the  bottles.  If  the  final 
rinse  water  is  clean  and  hot,  and  the  steam  is  ap- 
plied long  enough,  the  bottles  leave  the  machine 
at  a  temperature  of  from  150°  to  170°,  and  are 
reasonably  free  from  bacteria. 

Several  points  are  to  be  borne  in  mind  in  using 
a  machine  of  this  kind.  In  the  first  place,  no  ma- 
chine can  be  depended  upon  to  fully  clean  an 
extremely  dirty  bottle,  particularly  those  which  are 
returned  from  the  bottle  exchanges  and  the  dumps. 
Such  bottles  should  first  be  washed  by  hand  upon 
revolving  brushes,  where  they  can  be  clearly  seen 
by  the  workman.  They  should  then  be  washed  again 
in  the  regular  jet- washing  machine.  Another  im- 
portant point  is  that  the  perforations  in  the  wash- 
ing plates  are  liable  to  become  clogged  either  with 
particles  of  dirt,  or  with  rust,  or  it  may  be  with 
deposits  which  are  thrown  down  from  water  which 
is  very  hard.  If  these  openings  are  stopped  up 
it  will  mean  that  some  bottles  are  not  washed  as 
it  is  intended  they  should  be,  and  dealers  may  be 
unable  to  account  for  an  unusually  large  number 
165 


THE    PASTEURIZATION    OF    MILK 

of  dirty  bottles  which  they  find  from  time  to  time 
upon  their  routes. 

Another  important  item  is  the  temperature  of 
the  rinsing  water.  Unless  this  temperature  is  con- 
trolled by  a  thermostat,  it  may  be  easy  to  care- 
lessly let  the  temperature  drop  below  the  steriliz- 
ing point.  Workmen  who  have  to  take  away  the 
washed  bottles  from  the  machine  and  store  them 
find  that  it  is  uncomfortable  to  handle  bottles  which 
are  extremely  hot,  and  these  men  may,  therefore, 
allow  the  steam  supply  to  the  rinsing  tank  to  be 
cut  down  to  such  an  extent  that  the  bottles  do  not 
get  sterilized.  A  thermostat  attached  to  this 
rinsing  tank  will  automatically  keep  the  tempera- 
ture up  to  the  desired  point.  If,  in  addition  to 
this,  a  temperature  recorder  is  also  attached  to  this 
tank,  a  record  will  be  kept  which  a  dealer  may 
keep  on  file  as  an  office  record..  This  will  enable 
him  to  keep  in  closer  touch  with  the  work  which 
is  being  done  in  his  washing-room. 

Another  important  matter  is  to  make  sure  that 
the  water  which  is  used  for  the  final  rinse  water 
is  fresh,  clean  water,  and  that  it  is  not  used  over 
and  over  in  the  final  rinse  tank.  Most  of  the 
newer  machines  are  so  arranged  that  the  water 
166 


FROM    THE    PRACTICAL    VIEWPOINT 

which  is  forced  into  the  bottles  for  the  final  rinse, 
instead  of  falling  back  into  the  tank  from  which 
it  is  pumped,  is  carried  back  into  the  tank  behind 
it.  From  here  it  can  be  properly  used  for  the  pre- 
liminary rinsing  of  the  bottles.  The  use  of  fresh, 
clean  water  for  final  rinsing  is  somewhat  expen- 
sive when  a  public  water  supply  is  used,  and  also 
a  good  deal  of  steam  is  required  to  heat  it,  but  in 
order  to  obtain  sterile  bottles  it  is  necessary.  For 
heating  this  water  use  can  be  made  of  the  exhaust 
steam  from  engines  and  pumps,  and  thus  heating 
expenses  may  be  cut  down. 

There  is  one  form  of  automatic  washing  ma- 
chine in  which  the  bottles  which  are  being  treated 
are  forced  down  into  successive  tanks  of  water,  and 
the  inverted  bottles  are  pushed  over  fingers  from 
which  water  is  forced  in  a  direction  somewhat 
tangent  to  and  also  at  right  angles  to  the  inserted 
finger.  The  water  as  it  is  forced  into  the  bottle 
has  therefore  somewhat  of  a  scouring  action.  This 
is  of  advantage  in  removing  dirt  which  has  ad- 
'Jiered  to  the  glass.  In  this  machine,  also,  the 
water  which  is  used  for  the  final  rinse  is  heated 
under  pressure,  and  as  a  result,  when  it  is  forced 
into  the  bottle,  its  temperature  is  frequently  above 

167 


THE    PASTEURIZATION    OF    MILK 

the  boiling  point.  One  feature  of  this  machine 
is  unique.  The  machine  is  so  constructed  that, 
when  the  final  rinse  water  falls  below  a  definite 
temperature,,  of  say  180°,  it  refuses  to  operate, 
since  the  bottles  will  not  be  lifted  from  the  rinse 
tank,  but  will  remain  submerged.  The  machine 
thus  becomes  its  own  thermostat.  This  effect  is  pro- 
duced in  the  following  manner:  The  platform 
upon  which  the  cases  are  placed,  and  by  means  of 
which  they  are  lowered  into  and  lifted  from  the 
rinsing  tank,  is  so  counterbalanced  that  when  the 
bottles  are  full  of  water  the  weight  is  too  great 
for  the  case  to  be  lifted.  If  the  water  which  is 
forced  into  the  bottles  is  hot  enough  so  that  as  re- 
leased from  pressure  it  is  converted  into  steam, 
then  the  water  is  forced  out  of  the  bottles,  and  they 
have  sufficient  buoyancy  to  enable  the  counter- 
weight to  lift  the  entire  case  out  of  the  tank. 

The  older  method  used  in  washing  bottles,  even 
when  large  quantities  were  handled,  was  to  pro- 
vide means  for  soaking  the  dirty  bottles,  then  to 
wash  them  by  hand  on  revolving  brushes,  and 
finally  to  sterilize  them  in  separate  rooms,  or  in 
tanks  into  which  live  steam  was  discharged  for  a 
considerable  time.  This  method  is  still  in  use  to 
168 


FROM    THE    PRACTICAL    VIEWPOINT 

a  considerable  extent  and  is  effective,  but  is  more 
expensive  than  the  machine  method.  This  added 
expense  is  principally  due  to  the  amount  of  labor 
involved  in  the  many  handlings  of  the  bottles 
which  is  necessary.  Various  soaking  machines  are 
in  use.  Some  of  them  are  so  arranged  that  it  is 
not  necessary  for  the  workmen  to  put  their  hands 
into  the  soaking  solution,  since  an  endless  con- 
veyor carries  the  bottles  into  and  out  of  the  soak- 
ing tank.  The  solution  is  made  so  strong  that  all 
foreign  matter,  even  the  bottle  caps,  is  disinte- 
grated. After  being  removed  from  the  soaker,  a 
rinsing  by  means  of  a  machine  which  forces  hot 
water  into  them  renders  them  sterile. 

Some  method  of  thorough  hand  washing  with 
subsequent  careful  sterilizing  probably  gives  bet- 
ter results  than  does  machine  work,  provided  the 
men  who  do  the  washing  are  careful  to  see  that  no 
dirty  bottles  get  by  them.  This  is  an  expensive 
method  of  cleaning  bottles. 

Whatever  method  of  washing  is  employed,  care- 
ful attention  should  be  given  to  proper  inspection 
of  the  washed  bottles.  Probably  no  one  thing  can 
do  more  harm  to  a  milkman's  business  than  for  his 
customers  to  frequently  find  bottles  which  have 


THE    PASTEURIZATION    OF    MILK 

dirt  adhering  to  the  inside  of  them.  Even  though 
the  dirt  may  have  been  sterilized  by  the  steam 
treatment  and  be  therefore  harmless,  the  custom- 
er's sense  of  cleanliness  is  offended  and  the  dealer 
may  lose  his  trade. 

A  practice  which  has  been  adopted  by  some 
dealers  commends  itself  to  the  careful  milkman. 
This  is  the  practice  of  restirilizing  the  bottles  after 
they  have  been  inspected  and  all  dirty  ones  re- 
moved. Any  contamination  which  may  have  re- 
sulted from  the  handling  of  the  bottles  by  the 
workmen  will  thus  be  remedied. 

After  treatment,  washed  bottles  should  be  stored 
either  in  an  inverted  position  until  they  are  used, 
or  else  they  should  be  protected  by  suitable  cov- 
ers or  by  placing  them  in  separate  rooms  where  no 
infection  can  occur.  If  a  cold-storage  room  is 
provided,  for  the  washed  bottles,  there  is  a  cer- 
tain advantage.  When  it  is  remembered  that  the 
mass  of  glass  in  a  milk  bottle  nearly  equals  the 
mass  of  the  milk  contained  in  it,  it  can  be  seen 
that  if  the  bottle  is  warm,  before  it  is  filled,  the 
temperature  of  the  milk  will  be  raised  to  a  con- 
siderable extent.  When  empty  bottles  are  stored 
at  room  temperature  in  the  summer,  they  may 
170 


FROM    THE    PRACTICAL    VIEWPOINT 

have  a  temperature  of  65°  to  70°  when  the  milk 
goes  into  them.  If  milk  is  cooled  by  the  cooler 
no  lower  than  50°,  it  will,  by  coming  in  contact 
with  the  warm  bottle,  be  warmed  to  a  temperature 
of  from  55°  to  60°.  Bacteria  troubles  may  fol- 
low, especially  if  the  cases  of  bottled  milk  are  not 
immediately  iced,  or  if  they  are  placed  in  a  cold 
room  without  ice  being  placed  in  contact  with  the 
bottles. 

It  is  a  known  fact  that  milk  either  in  cans  or 
bottles  will  be  very  slow  in  cooling  if  the  con- 
tainers are  placed  in  dry  air,  even  though  the  tem- 
perature of  the  air  is  considerably  below  that  of 
the  milk.  Milk  containers,  however,  which  have 
ice  placed  upon  them,  will  become  cooled  in  a  short 
time. 

Dealers  and  others  have  not  realized  to  what  an 
extent  unclean  cans  and  covers  may,  and  in  fact 
do,  affect  the  bacterial  content  of  the  milk.  Un- 
til comparatively  recently,  no  effective  can  wash- 
ing, sterilizing  and  drying  machines  have  been 
placed  on  the  market,  and  even  now  comparatively 
few  milk  dealers  are  using  them  to  the  extent  to 
which  their  merit  entitles  them.  It  is  usually  found 
that  in  milk-handling  plants,  both  in  those  where 

171 


THE    PASTEURIZATION    OF    MILK 

the  milk  is  pasteurized  and  in  those  from  which  the 
milk  is  shipped  in  the  raw  state,  the  sterilizing  is 
very  inadequately  done.  Usually  the  cans  are 
washed  by  hand  with  a  brush,  and  are  then  placed 
over  a  single  jet  of  rinsing  water  and  then  over  a 
single  jet  of  live  steam.  The  time  occupied  in 
both  rinsing  and  steaming  is  usually  but  a  few 
seconds.  It  often  happens  that  the  can  covers  are 
not  steamed  at  all,  but  are  simply  rinsed  in  water 
which  is  not  over  clean.  When  the  cans  which 
are  to  be  returned  to  the  patrons  are  washed,  the 
steaming  which  the  cans  receive  is  so  brief  that  it 
is  almost  negligible.  This  is  not  altogether  the 
fault  of  the  man  who  is  washing  the  cans,  for 
when  milk  is  being  delivered  rapidly  to  the  plant 
there  is  little  time  for  long  steaming.  As  a  matter 
of  fact,  the  cans  require  a  more  careful  cleansing 
and  sterilizing  than  do  the  bottles,  since  they  are 
more  likely  to  contain  crevices  and  uneven  sur- 
faces than  are  the  bottles.  If  for  any  reason  it  is 
not  feasible  for  a  dealer  to  install  an  automatic 
can  washer,  it  is  still  possible  to  obtain  satisfac- 
tory results.  An  apparatus  which  is  comparatively 
inexpensive  may  be  constructed  by  providing  a  long 
table  or  runway  of  iron  plate  on  which  there  are 
172 


FROM    THE    PRACTICAL    VIEWPOINT 

installed  two  or  three  jets  of  water  for  rinsing  cans, 
and  also  three  or  more  jets  of  steam.  Each  jet 
should  be  provided  with  an  automatic  valve  which 
will  be  opened  by  the  weight  or  pressure  of  the 
can  as  it  is  placed  over  the  jet.  If  flanges  of  iron 
or  sections  of  gas  pipe  are  so  attached  to  the  table 
that  they  will  engage  the  flare  of  the  can  mouth 
as  it  is  inverted  over  the  table,  it  will  be  impos- 
sible to  remove  the  can  until  it  has  travelled  entire 
length  of  the  table  and  has  thus  received  the 
influx  of  water  and  steam  from  each  of  the  jets. 
It  is  possible  to  so  arrange  the  table  that  both 
cans  and  covers  will  be  treated  at  the  same  time  on 
the  same  table.  This  is  accomplished  by  install- 
ing two  sets  of  gas-pipe  guides,  one  of  them  to 
hold  the  cans  in  place  and  the  other  of  them  to  be 
just  above  the  covers  as  they  are  pushed  along  the 
table,  with  the  open  end  down.  The  cans  referred 
to  in  this  connection  are  the  standard  forty-quart 
cans  used  most  largely  in  the  East. 

Various  machines  are  on  the  market  which  are 
so  arranged  that  the  cans,  after  having  been  well 
steamed,  are  also  dried  by  means  of  a  blast  of 
heated  air.  This  drying  is  important  for  two 
reasons.  First,  because  the  moisture  which  may 
173 


THE    PASTEURIZATION    OF    MILK 

be  left  in  the  can  renders  the  condition  favorable 
for  the  growth  of  bacteria  which  have  escaped  de- 
struction, and  second,  because  cans  which  are  not 
dry  are  much  more  likely  to  become  rusty.  Rusty 
cans  are  hard  to  clean,  and  frequently  become  a 
loss  to  the  owner  because  they  soon  wear  out  and 
are  discarded.  One  form  of  can  rinser,  steamer 
and  dryer  is  rather  ingeniously  arranged.  The  ex- 
haust steam,  after  having  been  used  to  operate  a 
turbine-driven  fan,  is  employed  to  sterilize  the 
cans.  The  steam  pipe  which  supplies  the  fan  tur- 
bine passes  in  coils  through  an  air  chamber,  and 
thus  is  used  to  heat  the  air  which  is  forced  by  the 
fan  into  the  cans  after  they  have  been  sterilized. 
There  is  thus  a  very  economical  use  of  the  steam, 
and  the  apparatus  is  also  very  compact. 

Cans,  after  they  have  been  treated,  should  be 
stored  in  an  inverted  position  until  they  are  used 
for  containing  milk.  If,  however,  they  are  thor- 
oughly dry,  there  seems  to  be  no  objection  if  the 
covers  are  tightly  placed  upon  them  and  they  are 
then  stored  without  inverting. 

In  determining  what  test  to  apply  in  order  to 
ascertain  whether  or  not  milk  containers  are  ster- 
ile, or  sufficiently  so  for  practical  purposes,  it 
174 


FROM    THE    PRACTICAL    VIEWPOINT 

should  be  remembered  that  we  are  not  dealing 
with  laboratory  conditions,  and  that  therefore  ab- 
solute sterility  is  not  necessary,  however  desirable 
it  may  be  from  a  theoretical  standpoint.  Our  milk 
itself  is  not  sterile,  and  if  we  can  be  assured  that 
the  containers  are  sufficiently  clean  so  that  they 
will  not  add  any  appreciable  amount  of  bacteria  to 
the  milk,  and  that  those  which  may  be  added  are 
not  of  a  pathogenic  character,  then  health  authori- 
ties should  be  satisfied.  Remembering  that  a  quart 
of  milk  contains  about  one  liter  of  fluid,  or  1,000 
cubic  centimeters,  it  seems  reasonable  to  allow  the 
washed  bottles  to  contain  1,000  bacteria.  This 
would  add  but  one  bacterium  to  each  c.c.  of  milk 
contained  in  the  filled  bottle.  In  like  manner, 
40,000  bacteria  in  a  washed  can  might  add  the 
same  amount  of  bacterial  contamination  to  the 
forty  quarts  of  milk  contained  in  the  filled  can. 
If  none  of  these  were  of  the  coli  group,  it  is  proba- 
ble that  no  danger  would  result.  As  a  matter  of 
fact,  with  methods  of  cleansing  which  may  be  easily 
secured,  the  bacterial  content  of  the  containers  will 
be  much  less  than  the  allowable  amount  above  re- 
ferred to. 


175 


THE    PASTEURIZATION    OF    MILK 

Bottle-Filling 

The  filling  of  the  bottles  is  more  an  economic 
problem  than  a  sanitary  one.  Of  course,  the  care- 
ful cleaning  and  sterilization  of  the  apparatus  is 
necessary,  no  matter  what  kind  of  filler  is  used. 
Any  failure  in  this  respect  may  cause  the  milk  to 
gather  up  bacteria  while  it  passes  through  the 
bottling  machine.  This  may  cause  annoyance,  at 
least,  when  tests  are  made  which  indicate  a  high 
bacterial  content.  If,  however,  the  cleaning  is 
carefully  done,  the  items  which  most  interest  the 
milk  men  are  the  questions  of  expense  and  of  effi- 
ciency in  operation. 

If  a  machine  is  operated  by  hand  power,  there 
is  the  question  whether  human  power  is  cheaper 
than  machine  power.  If  automatically  operated 
by  outside  power,  either  electric,  steam  or  hydrau- 
lic, then  the  matter  of  bottle  breakage,  case  dam- 
age, and  loss  of  milk  from  broken  bottles  is  an 
important  consideration.  A  power-driven  machine 
may  or  may  not  be  slower  in  operation  than  hand 
power.  The  conditions  surrounding  each  plant 
must  be  considered  and  decisions  made  in  accord- 
ance with  them. 

176 


FROM    THE    PRACTICAL    VIEWPOINT 

The  rotary  filler  and  capper  is  coming  into  quite 
extensive  use,  with  many  features  about  it  which 
appeal  strongly  to  the  milkman. 

Bottle-Capping 

It  is  important  that  milk,  after  having  been 
pasteurized,  shall  not  be  recontaminated  in  any 
way.  If  containers  are  properly  cleaned,  the  great- 
est danger  of  such  reinfection  lies  in  the  practice 
of  capping  bottles  by  hand.  When  this  method  of 
capping  is  employed,  the  caps  are  frequently  kept 
in  open  boxes  beside  the  bottling  machine,  and  they 
are  sometimes  kept  in  the  pockets  of  the  workmen 
who  are  capping  the  bottles.  There  is  thus  con- 
stant danger  that  the  caps  will  become  infected  by 
dust  in  the  air,  by  milk  which  is  spattered  upon 
them  or  by  means  of  the  hands  of  the  persons  who 
handle  them.  Men  who  handle  bottle  cases  and  at 
the  same  time  work  about  machinery  cannot  easily 
keep  the  hands  clean.  The  milk  caps  then  suffer. 
If  any  germs  of  disease  are  about  these  employees 
then  the  danger  becomes  apparent. 

Some  form  of  capping  machine  is  desirable.  Sev- 
eral such  are  on  the  market,  and  many  of  them 

177 


THE    PASTEURIZATION    OF    MILK 

are  doing  satisfactory  work.  It  is  not  necessary  to 
describe  the  characteristics  of  each.  Those  are 
most  desirable  which  fulfil  the  following  conditions : 

First:  The  caps  used  should  be  stored  in  sterile 
containers  or  tubes  before  they  are  inserted  in  the 
machine. 

Second:  A  very  small  percentage  of  the  bottles 
should  be  missed  in  capping. 

Third:  They  should  be  so  constructed  that  they 
can  be  readily  taken  apart  for  cleaning,  and  they 
should  have  no  concealed  pockets  or  spaces  where 
milk  is  likely  to  collect  and  become  sour  or  decom- 
posed. 

Fourth:  They  should  be  strongly  constructed  in 
order  that  they  may  stand  without  breakage  or  dis- 
arrangement, the  rather  rough  usage  to  which  they 
are  subjected. 

It  is  very  desirable  that  milk  bottles  be  sealed 
after  they  are  filled.  By  sealing  is  meant  that 
they  be  so  protected  that  they  cannot  be  opened 
without  the  fact  being  readily  detected  by  the  con- 
sumer. The  desirability  of  this  sealing  process 
gets  its  force  from  two  reasons: 

First:  To  prevent  the  drivers  or  others  from 
opening  the  bottles  and  adulterating  the  milk. 

178 


FROM    THE    PRACTICAL    VIEWPOINT 

Instances  have  been  known  where  the  drivers  of 
rival  companies  have  opened  the  bottles  belonging 
to  their  competitors,  and  have  fouled  the  milk  in 
order  to  cast  discredit  upon  the  milk  delivered  by 
the  rival  concern.  Other  drivers  have  taken  cream 
from  the  tops  of  bottles,  and  have  filled  the  bot- 
tles with  water.  The  cream  they  have  sold  for 
their  own  profit.  Bottles  which  were  effectively 
sealed  could  not  be  treated  in  this  way. 

Second :  To  prevent  possible  contamination  of  the 
milk  by  means  which  are  unintentional.  The  use  of 
the  usual  paper  plug  cap  leaves  a  space  above  the 
cap  where  dust  and  dirt  and  ice  water  from  melt- 
ing ice,  etc.,  can  collect.  Unless  this  is  carefully 
washed  off  before  the  bottle  is  opened,  it  is  likely 
to  fall  into  the  milk.  If  a  bottle  of  milk  which 
when  filled  has  a  temperature  of  say  50°  to  55° 
is  then  placed  in  a  case  and  covered  with  ice,  the 
milk  is  cooled  to  perhaps  35°  to  40°.  This  causes 
the  milk  to  contract.  The  air  in  the  space  above 
the  milk  also  contracts,  and  a  suction  is  thus  cre- 
ated. The  water  which  collects  on  the  top  of  the 
cap  is  then  drawn  into  the  bottle  around  the  edge 
of  the  cap,  taking  with  it  some  of  the  dirt  which 
may  have  collected  there. 

179 


THE    PASTEURIZATION    OF    MILK 

The  drivers  of  retail  delivery  wagons  who  han- 
dle the  reins,  care  for  the  horses  and  then  in  de- 
livering milk  grasp  the  bottles  by  the  neck,  are 
particularly  likely  to  leave  some  dirt  or  contami- 
nating material  upon  the  lips  of  the  bottles  over 
which  the  milk  will  be  poured.  Serious  infection 
may  result.  Caps  which  are  real  seals  and  which 
at  the  same  time  protect  the  neck  and  lips  are  on 
the  market,  but  are  rather  expensive.  They  are 
used  by  dealers  upon  special  grades  of  milk,  such 
as  Certified,  Grade  A,  etc.,  but  are  as  yet  too  costly 
to  be  used  upon  the  lower  or  common  grade  of 
market  milk.  A  great  many  attempts  have  been 
made  to  devise  a  safe  seal  which  shall  be  protec- 
tive and  shall  be  inexpensive,  but  none  have  been 
very  successful.  A  fortune  awaits  the  man  who 
can  produce  a  satisfactory  seal  of  this  character. 

Paper  Bottles 

For  fifteen  years  or  more  various  sorts  of  paper 
milk  bottles  have  been  upon  the  market.  They 
have  been  made  in  various  forms.  Some  were 
made  of  pulp  which  was  formed  into  the  shape  of 
an  ordinary  bottle.  Some  have  been  crimped  into 
180 


FROM    THE    PRACTICAL    VIEWPOINT 

a  bottle  form  from  a  single  sheet  of  heavy  paper. 
Others  have  been  made  of  heavy  waxed  paper, 
through  which  the  cream  was  visible.  Some  have 
had  straight  parallel  sides.  They  have  been  made 
round  and  square;  have  been  filled  from  the  top, 
and  have  been  filled  from  the  bottom,  but  the  suc- 
cess which  has  attended  them  has  not  been  very 
marked,  especially  in  the  East.  There  are  some 
firms  in  the  western  part  of  the  country  where 
their  use  has  been  rather  extensive  and  where  they 
are  said  to  be  satisfactory. 

The  objections  to  their  use  has  been — 1st,  the 
expense.  They  are  more  costly  than  are  glass 
bottles,  when  it  is  considered  that  the  glass  bottle 
is  used  repeatedly,  while  the  paper  one  is  used 
but  once. 

2nd.  Many  of  them  are  not  strong  enough  to 
endure  the  heavy  icing  and  rough  handling  to 
which  they  are  subjected. 

3rd.  Customers  have  been  accustomed  to  seeing 
the  cream  in  the  bottle,  and  object  to  bottles  where 
the  cream  is  out  of  sight. 

4th.  The  constantly  increasing  cost  of  paper 
renders  it  questionable  whether  the  equipment  for 
.using  paper  bottles  may  not  prove  to  be  available 
181 


THE    PASTEURIZATION    OF    MILK 

for  a  short  time  only,  and  its  expense  thus 
wasted. 

5th.  There  is  always  uncertainty  concerning  the 
cleanliness  of  the  bottles  as  delivered  by  the  manu- 
facturers for  use,  and  also  as  to  whether  or  not 
the  material  used  in  the  paper  may  affect  the  milk. 

There  are  undoubted  advantages  in  the  use  of 
the  paper  container,  among  which  are: 

1st.  That  the  expense  of  handling  and  trans- 
portation will  be  lessened,  on  account  of  the  lesser 
weight  of  the  paper. 

2nd.  The  expense  of  washing  returned  bottles 
will  be  saved,  since  the  paper  container  will  be 
used  but  once. 

3rd.  The  possible  danger  which  exists  through 
the  return  of  bottles  from  the  public  dumps,  and 
from  houses  in  which  there  are  communicable  dis- 
eases will  be  lessened  if  the  single  service  container 
is  used. 

4th.  The  danger  from  broken  glass,  which  occa- 
sionally finds  its  way  into  the  milk,  will  be  ob- 
viated, and  the  wounds  which  are  inflicted  by 
broken  bottles  upon  workmen  who  handle  and  wash 
them  will  be  prevented. 


FROM    THE    PRACTICAL   VIEWPOINT 

Home  Pasteurization 

Many  physicians  who  thoroughly  believe  that 
milk  should  be  pasteurized  for  infant  feeding,  also 
recommend  that  this  pasteurization  be  performed 
in  the  home,  and  that  the  pasteurized  milk  be 
fed  as  quickly  as  possible  after  the  heating  is 
completed.  This  method  eliminates  the  possibil- 
ity of  recontamination  which  may  occur  when  milk 
is  handled  under  commercial  conditions,  and  it  also 
insures  that  those  bacteria  which  are  not  destroyed 
during  the  pasteurization  process  will  have  little 
opportunity  for  growth  and  increase  between  the 
pasteurization  of  the  milk  and  its  consumption. 

It  is  not  the  purpose  of  the  writer  to  here  de- 
scribe the  various  methods  employed  for  home  pas- 
teurization. Such  information  may  be  obtained 
from  the  pamphlets  which  are  distributed  by  those 
responsible  for  maintaining  the  various  infant- feed- 
ing stations  located  in  our  cities.  Some  of  these 
stations  are  maintained  by  the  municipalities  and 
some  by  private  individuals.  Dr.  Rosenau,  in  his 
book  on  "The  Milk  Question,"  discusses  this  phase 
of  pasteurization  quite  fully. 

Whatever  method  of  home  treatment  is  employed, 
183 


THE    PASTEURIZATION    OF    MILK 

care  should  be  taken  that  the  heat  is  high  enough 
and  is  maintained  for  a  sufficient  time  to  reach  all 
parts  of  the  milk,  and  so  kill  the  pathogenic  bac- 
teria. The  heating  medium  should  not  be  hot 
enough  to  cook  or  change  the  chemical  characteris- 
tics of  the  milk  or  to  impart  to  it  a  disagreeable 
odor  or  taste. 


184, 


CHAPTER    VI 

EFFICIENCY    OF    VARIOUS    APPARATUS 

During  the  writer's  experience  in  the  actual 
operation  of  pasteurizing  plants,  a  great  many  sam- 
ples of  milk  have  been  taken  which  have  been  ex- 
amined for  their  bacterial  content  in  order  to  de- 
termine the  efficiency  of  the  various  pasteurizing 
plants  in  the  destruction  of  bacteria.  These  results 
have  been  tabulated,  showing  the  bacterial  content 
before,  during  and  after  pasteurization.  In  these 
tables  the  kind  of  apparatus  are  indicated  by  fig- 
ures only,  no  name  of  apparatus  or  of  the  manu- 
facturers being  given.  The  dealers  at  whose  plants 
the  tests  were  made  are  indicated  as  "A,"  "B," 
"C,"  etc.  Thus  at  a  plant  operated  by  dealer 
"A,"  for  instance,  a  heater  illustrated  by  Fig.  00, 
a  holder  like  Fig.  00,  and  a  cooler  like  Fig.  00  may 
have  been  employed. 

Lest  the  reader  be  misled  as  to  the  efficiency 
of  certain  definite  forms  of  apparatus,  and  lest  cer- 
tain manufacturers  be  led  to  feel  that  results  ob- 
tained have  failed  to  give  justice  to  the  apparatus 
185 


THE    PASTEURIZATION    OF    MILK 

handled  by  them,  the  reader  is  warned  that  effi- 
ciency tests  are  sometimes  misleading.  It  should 
be  remembered  that  at  least  four  factors  enter  into 
the  causes  which  produce  the  effects  indicated. 

1st.    The  character  of  the  apparatus  itself. 

2nd.  The  carefulness  with  which  the  plant  is 
operated  by  those  responsible  for  it. 

3rd.  Whether  the  apparatus  is  thoroughly 
cleaned  and  sterilized. 

4th.    The  character  of  the  milk  treated. 

It  is,  of  course,  understood  by  all  those  familiar 
with  bacteriological  work  that  these  are  factors  of 
error  in  the  results  which  can  never  be  entirely 
overcome. 

If  apparatus  is  so  constructed  that  the  heating 
and  holding  and  cooling  are  true  to  their  indicated 
capabilities,  then  the  results  will  be  good — if  the 
machine  is  properly  operated  and  if  it  is  clean. 
These  factors  being  reliable,  the  results  can  be 
taken  at  their  face  value  if  the  milk  is  of  normal 
quality  and  does  not  contain,  we  will  say,  certain 
forms  of  bacterial  life  which  are  difficult  to  destroy. 

When  results  are  good,  it  undoubtedly  means 
that  both  the  apparatus  and  its  operation  are  sat- 
isfactory. If  the  results  are  bad,  it  is  not  always 
186 


FROM    THE    PRACTICAL    VIEWPOINT 

easy  to  say  whether  the  machine,  its  operation,  or 
the  milk  is  at  fault. 

In  regard  to  the  milk  itself,  there  are  many  fac- 
tors which  must  be  taken  into  account  when  de- 
termining the  efficiency  of  any  apparatus.  Esti- 
mates of  machine  efficiency  based  upon  the 
percentage  of  bacteria  destroyed  are  frequently 
misleading.  It  can  be  readily  seen  that  if  the  bac- 
terial content  of  the  raw  milk  is  high,  any  good 
pasteurizer  will  kill  a  large  percentage  of  the 
germs  in  the  milk.  For  instance,  if  the  original 
milk  contained  5,000,000  bacteria  per  c.c.,  and 
after  being  pasteurized  contains  100,000  bacteria, 
there  would  have  been  a  reduction  of  98  per  cent, 
of  the  bacteria  in  the  original  milk.  Milk  contain- 
ing 100,000  bacteria  per  c.c.  would  not,  however, 
be  considered  to  be  an  entirely  satisfactory  prod- 
uct to  place  upon  the  market,  especially  if  it  con- 
tained organisms  of  the  coli  type. 

Again,  let  us  suppose  that  the  original  milk  con- 
tained 10,000  per  c.c.,  and  that  by  means  of  the 
pasteurizing  process  this  number  was  reduced  to 
1,000;  such  a  milk  would  undoubtedly  be  a  proper 
milk  for  consumption,  although  the  percentage  of 
reduction  had  been  QO  per  cent  only.  It  is  there- 

187 


THE    PASTEURIZATION    OF    MILK 

fore  plainly  seen  that  the  efficiency  of  pasteuriz- 
ing machinery,  when  expressed  in  percentage  re- 
duction of  bacteria  only,  must  be  taken  with  a 
great  deal  of  reserve.  It  is  necessary  to  know  the 
character  of  the  raw  milk,  and  also  to  know  if  coli 
types  are  all  destroyed.  In  speaking  of  the  de- 
struction of  coli,  it  should  be  remembered  that 
germs  of  this  group  are  not  necessarily  all  danger- 
ous. In  this  connection  they  are  used  as  indicators 
only.  It  is  known  that  they  are  more  difficult  to  de- 
stroy than  are  any  of  the  pathogenic  or  disease-pro- 
ducing bacteria.  If,  therefore,  the  coli  are  all 
killed,  it  is  safe  to  assume  that  no  dangerous  mi- 
crobes remain  alive.  While,  if  the  coli  are  present 
in  the  finished  product,  there  is  a  possibility  that 
disease  germs  are  also  present.  It  is  known  pretty 
definitely  that  if  milk  is  heated  to  142-145°  for 
thirty  minutes,  all  coli  will  be  destroyed. 

The  following  tables  are  compiled  from  very 
many  tests  made.  When  these  tests  were  made 
there  were  three  or  four  samples  of  milk  taken  at 
each  point  of  examination;  for  instance,  four  sam- 
ples of  raw  milk  were  taken  at  the  same  time. 
When  these  were  examined,  the  average  of  all  the 
counts  was  determined.  In  the  same  way  there 
188 


FROM    THE    PRACTICAL    VIEWPOINT 

were  four  samples  taken  at  the  outlet  of  the  heater, 
the  holder,  and  so  on.  In  the  tables  herewith  com- 
piled, only  the  average  counts  are  indicated,  in  or- 
der to  avoid  any  bewildering  mass  of  figures.  It 
should  be  therefore  borne  in  mind  that  bacteria 
counts  here  indicated  are  averages. 

In  figuring  out  the  percentage  of  reduction, 
the  relation  between  the  bacterial  content  of  the 
raw  milk  and  the  milk  as  it  leaves  the  holder  is 
considered.  It  will  frequently  be  found  that  the 
number  of  bacteria  in  the  milk  leaving  the  cooler 
is  higher  than  when  it  leaves  the  holding  appara- 
tus, and  that  this  number  is  again  increased  when 
the  milk  enters  the  bottles  and  cans.  Usually  un- 
clean coolers,  bottling  machines  and  bottles  are 
responsible  for  this  increase. 

Not  all  of  the  types  of  apparatus  which  are 
illustrated  and  described  in  this  book  have  been 
tested  by  the  writer  as  to  their  efficiency  in  the  de- 
struction of  bacteria,  and  any  omissions  which  may 
be  observed  in  the  tables  are  not  due  to  any  inten- 
tion on  the  part  of  the  writer  to  slight  any  of  them, 
or  to  any  desire  to  call  attention  more  forcibly 
to  one  kind  of  machine  than  to  another.  It  simply 
means  that  the  results  of  tests  are  not  available. 
189 


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207 


CHAPTER    VII 

CHANGES    IN    THE    CREAM    LINE    DUE    TO    THE 
PASTEURIZATION     OF     MILK 

Dealers  who  have  had  experience  in  the  pas- 
teurization of  milk  know  that  from  time  to  time 
they  have  trouble  with  what  is  known  in  the  trade 
as  the  "cream  line"  upon  bottled  milk.  This  may 
mean  that  the  line  of  demarcation  between  the 
cream  in  the  bottle  and  the  skim  milk  just  below  it 
is  indistinct  and  faint,  or  it  may  mean  that  no 
cream  at  all  is  visible  and  the  contents  of  the  bot- 
tle has  the  same  color  all  the  way  through.  Again, 
it  may  mean  that  the  apparent  amount  of  cream 
upon  the  milk  is  lessened.  Either  one  of  these 
conditions  is  a  reason  for  complaint  on  the  part  of 
the  customers.  Dealers  are  therefore  anxious  to 
obtain  as  great  a  volume  of  cream  as  possible  upon 
the  milk  sold  by  them,  and  are  also  anxious  to  get 
the  line  of  division  as  distinct  as  possible.  Deal- 
ers are  sometimes  at  a  loss  to  know  why  milk  will 
at  one  time  show  a  good  cream  line,  and  at  another 
time,  when  the  conditions  are  apparently  the  same, 
the  cream  will  be  disturbed. 
208 


FROM    THE    PRACTICAL    VIEWPOINT 


In  1914,  when  the  writer  was  connected  with 
the  New  York  City  Department  of  Health,  the 
Board  of  Health  adopted  certain  modifications  in 
the  regulations  which  had  been  in  force  concerning 
the  pasteurization  of  milk.  Among  these  changes 
were  different  rules  concerning  the  temperature  to 
which  milk  must  be  heated  and  the  length  of  time 
for  which  it  must  be  held  at  this  temperature  if 
it  was  to  be  officially  recognized  as  pasteurized 
milk. 

Prior  to  that  time,  the  rules  allowed  a  somewhat 
wide  variation  in  the  heating  temperatures,  and  a 
corresponding  variation  in  the  length  of  time  for 
which  the  milk  should  be  held.  Thus  milk  which 
was  heated  to  140°  must  be  held  at  least  twenty 
minutes,  while  milk  heated  to  158°  need  be  held 
but  three  minutes.  Between  these  extremes  other 
temperatures  and  holding  times  were  allowed.  This 
sliding  scale,  as  it  might  be  called,  allowed  such  a 
latitude  that  milkmen  who  sold  milk  in  cans  only, 
and  were  thus  not  much  concerned  with  the  cream 
line,  could  heat  the  milk  to  a  high  temperature  and 
hold  it  for  a  short  time.  On  the  other  hand,  those 
dealers  who  sold  bottled  milk,  and  who  were  desir- 
ous to  obtain  as  great  a  volume  of  cream  as  pos- 
209 


THE    PASTEURIZATION    OF    MILK 

sible,  could  and  usually  did  heat  the  milk  to  a  low 
temperature  and  hold  it  for  a  comparatively  long 
time. 

A  desire  for  uniformity  of  methods  in  the  treat- 
ment of  milk  led  the  authorities  to  adopt  regula- 
tions, in  accordance  with  which  one  standard  for 
pasteurization  only  was  applied,  in  all  cases  when 
milk  was  heated  for  market  use.  The  rules  thus 
adopted  required  all  pasteurized  milk  to  be  heated 
to  145°  for  thirty  minutes. 

Dealers  who  endeavored  to  comply  with  this  rule 
complained  that  they  found  the  cream  line  was 
affected,  and  that  they  could  not  comply  with  the 
public  requirements  without  injury  to  their  busi- 
ness. 

In  an  effort  to  ascertain  to  what  extent  the 
strict  enforcement  of  the  regulations  would  affect 
the  commercial  quality  of  the  milk,  the  writer  made 
an  investigation. 

This  investigation  was  not  made  with  the  inten- 
tion to  determine  what  form  of  apparatus  would 
do  the  best  work,  nor  to  make  any  extended  or  ex- 
haustive tests  of  any  one  form  of  apparatus  un- 
der varying  surroundings  and  conditions.  The  ob- 
ject was  to  see  if  it  was  possible  and  commercially 
210 


FROM    THE    PRACTICAL    VIEWPOINT 

practicable  to  heat  milk  to  145°  and  hold  it  for 
thirty  minutes  with  the  machines  in  use  in  the  city 
without  seriously  affecting  the  cream  line.  Any 
results  and  data  secured  do  not  warrant  the  con- 
clusions that  the  experiments  indicate  the  essential 
superiority  of  any  of  the  apparatus  described. 

A  little  thought  on  the  part  of  the  reader  will 
make  it  clear  that  so  many  factors  enter  into  the 
problem  that  such  conclusions  would  be  unwar- 
ranted. 

In  the  same  way  that  percentages  of  bacteria 
reduction  mean  little  unless  we  possess  all  the 
data  connected  with  the  handling  of  the  milk, 
so  likewise  percentages  of  cream  upon  pas- 
teurized milk  are  not  alone  of  ultimate  value  as 
showing  that  one  apparatus  is  more  satisfactory 
than  another. 

A  series  of  tests  was  made  at  several  of  the 
pasteurizing  plants  in  New  York  City  at  which 
different  forms  of  apparatus  were  being  used,  the 
milk  in  these  various  plants  being  subjected  to  dif- 
ferent degrees  of  temperature  for  varying  lengths 
of  time.  Samples  of  milk  were  taken  to  determine 
the  amount  of  cream  which  appeared  upon  the 
bottled  product.  At  the  same  time,  the  conditions 
211 


THE    PASTEURIZATION    OF    MILK 

surrounding  the  handling  of  the  milk  were  noted 
in  order  to  determine  if  other  factors  aside  from 
the  temperature  and  holding  time  had  any  effect 
upon  the  cream  line. 

In  making  the  tests,  the  samples  of  milk  taken 
were  set  in  standard  cream  gauge  glasses  and  the 
actual  percentage  of  cream  showing  upon  the  milk 
as  indicated  thereon  was  carefully  noted.  These 
tests  were  made  during  the  early  part  of  Decem- 
ber, 1914. 

FIRST  TEST. — The  first  test  was  made  at  a  plant 
in  which  the  pasteurizing  apparatus  consisted  of 
three  tanks  of  the  type  shown  in  Fig.  13.  Each 
tank  had  a  capacity  of  about  forty  cans  of  milk, 
and  after  being  filled  the  milk  was  heated  by 
means  of  a  revolving  coil  of  pipe  extending  through 
the  tank,  through  which  coil  hot  water  and  steam 
were  forced.  After  the  milk  reached  the  proper 
temperature,  the  steam  was  shut  off  in  this  coil 
and  the  milk  was  held  at  the  same  temperature 
for  the  desired  length  of  time.  It  was  then  dis- 
charged into  a  cooler  consisting  of  a  tank  in  which 
were  revolving  disks,  which  is  not  here  illustrated, 
and  immediately  cooled.  Since  it  required  con- 
siderable time  for  the  tank  to  be  fully  emptied 
212 


FROM    THE    PRACTICAL    VIEWPOINT 

after  the  discharge  was  commenced,  it  is  evident 
that  a  part  of  the  milk  was  held  in  the  tank  for 
a  considerably  longer  time  than  was  that  which 
was  first  discharged  from  the  tank.  In  making  the 
test,  one  tankful  of  milk  was  heated  to  a  tempera- 
ture of  142°  and  was  held  thereat  for  about  thirty 
minutes.  The  exact  time  of  holding  was  not  as- 
certained on  account  of  the  fact  that  the  milk  was 
being  discharged  from  the  tank  at  the  time  the 
inspection  began.  A  sample  was  taken  from  this 
milk  and  placed  in  a  cream  gauge,  which  was  then 
packed  in  ice  and  allowed  to  stand  for  four  hours, 
at  the  end  of  which  time  15  per  cent,  of  cream  ap- 
peared upon  the  cream  gauge. 

A  second  sample  was  taken  from  one  of  the 
tanks  in  which  the  milk  had  been  heated  to  a  tem- 
perature of  146°,  and  held  thereat  for  thirty-four 
and  a  half  minutes.  The  sample  here  taken  was 
allowed  to  stand  packed  in  ice  for  four  hours,  at 
the  end  of  which  time  13  per  cent,  of  cream  ap- 
peared upon  the  gauge.  A  third  sample  was  taken 
from  the  same  tank,  but  it  was  taken  from  that 
milk  which  was  last  discharged  from  the  tank. 
This  milk,  therefore,  had  been  held  in  the  tank  for 
one  hour  and  twenty-three  minutes.  This  sample 
213 


THE    PASTEURIZATION    OF    MILK 

was  also  set  in  ice  for  four  hours  and  showed  8  per 
cent,  of  cream  upon  the  gauge. 

A  fourth  sample  was  taken  from  a  second  tank 
in  which  the  milk  was  heated  to  a  temperature  of 
146°  and  held  thereat  for  exactly  thirty  minutes. 
This  milk  showed  15  per  cent,  of  cream  upon  the 
gauge. 

The  method  of  handling  the  milk  at  this  plant 
should  be  noted.  Milk  was  poured  from  the  cans 
into  a  dumping  tank  on  the  ground  floor.  It  was 
then  pumped  to  a  small  tank  upon  the  third  floor 
of  the  building,  thence  flowed  through  a  centrifugal 
clarifier,  such  as  shown  in  Fig.  32,  and  then  flowed 
directly  into  the  pasteurizing  tanks. 

SECOND  TEST. — A  test  was  also  made  in  another 
milk  plant  in  which  the  same  form  of  pasteurizing 
apparatus  was  installed.  In  this  plant,  the  milk 
was  pumped  from  the  receiving  vat  on  the  gound 
floor  into  a  tank  upon  the  second  floor,  from  which 
the  milk  flowed  through  a  clarifier  and  was  then 
discharged  into  a  mixing  vat,  from  which  it  flowed 
into  the  various  pasteurizing  tanks.  The  opera- 
tion of  this  plant  was  similar  to  that  in  the  plant 
previously  described,  except  that,  in  the  first  in- 
stance, the  water  which  was  forced  through  the 


FROM    THE    PRACTICAL    VIEWPOINT 

heating  coil  of  the  tank  was  heated  by  means  of  a 
steam  jet,  injecting  steam  directly  into  the  water 
pipe,  whereas,  in  the  second  instance,  water  was 
heated  in  a  tank  outside  of  the  pasteurizing  tank 
and  was  pumped,  after  the  heating,  directly  into 
the  heating  coil,  it  being  the  belief  that  if  the 
water  was  heated  in  this  manner  there  was  less 
danger  of  the  milk  becoming  scorched  on  account 
of  the  water  coil  having  been  heated  to  a  tempera- 
ture which  was  excessive 

At  this  second  plant  the  first  sample  was  taken 
from  the  raw  milk  before  it  had  passed  through 
the  clarifier.  This  sample  was  allowed  to  stand 
in  ice  for  eleven  hours,  at  the  end  of  which  time 
19l/2  per  cent,  of  cream  appeared  upon  the  gauge. 
A  Babcock  test  was  made  of  this  milk  and  it  was 
found  to  contain  3.8  per  cent,  of  butter  fat.  A 
second  sample  was  taken,  which  was  as  nearly  as 
possible  from  the  same  milk,  after  it  had  passed 
through  the  clarifier.  This  sample,  after  standing 
for  eleven  hours,  showed  17  per  cent,  of  cream  on 
the  gauge.  This  milk  also  contained  3.8  per  cent, 
of  butter  fat.  A  third  sample  was  taken  from  one 
of  the  pasteurizing  tanks  in  which  the  milk  was 
heated  to  145°  and  was  held  in  the  tank  for  thirty- 
215 


THE    PASTEURIZATION    OF    MILK 

three  minutes,  at  which  time  the  temperature  was 
found  to  be  14 2 y^°  F.  This  sample,  upon  being 
set,  showed  12  per  cent,  of  cream  in  the  cream 
gauge  and  contained  3.8  per  cent,  of  butter  fat. 
The  fourth  sample  was  taken  from  the  same  tank 
of  milk,  but  when  the  tank  was  nearly  empty. 
The  milk  had  been  standing  in  this  tank  for  one 
hour  and  twenty  minutes.  It  had  been,  however, 
cooled  to  a  temperature  of  60°  F.  by  means  of 
cold  water  pumped  through  the  revolving  coil. 
A  sample  of  this  milk,  upon  setting,  showed  15 
per  cent,  of  cream  in  the  cream  gauge  and  con- 
tained 3.8  per  cent,  of  butter  fat. 

It  was  thought  possible  that  the  speed  of  cool- 
ing of  milk  might  have  an  effect  upon  the  cream 
line.  Therefore  two  samples  of  milk  were  taken, 
one  of  which  had  a  temperature  of  135°  F.  This 
sample  was  allowed  to  stand  un-iced  until  cooled 
by  air  contact  to  a  temperature  of  about  40°  F. 
The  second  sample  of  milk  was  taken  from  the 
same  batch  of  heated  milk,  but  this  sample  was 
taken  after  the  milk  had  been  quickly  cooled  in 
the  cooling  apparatus  to  a  temperature  of  32°  F. 
After  setting,  these  two  samples  showed  no  appre- 
ciable difference  in  the  cream  content.  This  indi- 
216 


FROM    THE    PRACTICAL    VIEWPOINT 

cated  that  the   speed  of  cooling  had  little  or  no 
effect  upon  the  rising  of  the  cream  in  the  milk. 

The  tests  made  at  these  two  plants  indicated 
that  it  was  entirely  possible  to  heat  milk  to  145° 
F.  and  hold  it  for  thirty  minutes  without  materially 
affecting  the  volume  of  the  cream  contained  in  the 
bottled  milk,  and  that  milk  heated  to  145°  F. 
showed  the  same  amount  of  cream  as  that  which  is 
heated  to  142°  F. 

THIRD  TEST. — A  test  was  made  at  another  plant 
where  the  same  form  of  apparatus  for  pasteuriz- 
ing was  in  use.  During  this  test  a  sample  was 
taken  from  a  tank  in  which  the  milk  was  heated 
to  a  temperature  of  141°  and  held  there  for  sixty 
minutes.  This  sample,  after  standing  a  sufficient 
length  of  time,  showed  a  cream  content  of  15  per 
cent.  A  second  sample  was  taken  of  raw  milk 
which  had  already  been  passed  through  the  clari- 
fier,  and  this  milk  was  found  to  contain  15  per  cent, 
of  cream.  A  third  sample  was  taken  from  a  tank  in 
which  the  milk  had  been  heated  to  145°  and  held 
thereat  for  sixty  minutes.  This  milk,  after  stand^ 
ing,  showed  no  cream  at  all  upon  the  cream  gauge/ 

The  results  here  obtained  did  not  correspond 
with  those  obtained  at  the  two  other  plants  where 

217 


THE    PASTEURIZATION    OF    MILK 

the  same  apparatus  was  in  use.  No  apparent  rea- 
son could  be  seen  for  the  variation.  Milk  at  this 
plant,  as  received  from  the  patrons,  was  allowed 
to  flow  from  the  weigh  vat  into  the  mixing  vat, 
from  which  it  was  pumped  to  a  vat  upon  the  sec- 
ond floor,  thence  it  flowed  into  a  clarifier,  from 
which  it  was  discharged  into  a  large  mixing  vat  on 
the  same  floor.  It  then  flowed  by  gravity  to  the 
pasteurizing  vats  on  the  first  floor. 

FOURTH  TEST. — A  further  test  was  made  at  an- 
other pasteurizing  plant,  in  which  the  milk  was  pas- 
teurized by  means  of  a  heater  and  holder,  shown 
in  Figs.  5  and  22.  In  this  heater  the  milk  was 
forced  between  two  concentric  cylinders,  in  each 
of  which  hot  water  was  contained,  having  a  tem- 
perature of  159°.  The  milk  while  being  heated 
was  kept  in  agitation  by  the  rapid  revolution  of 
one  of  the  cylinders  above  referred  to.  After 
heating,  the  milk  flowed  by  gravity  into  a  series  of 
insulated  tanks,  in  each  of  which  it  was  held  for 
twenty-four  minutes.  On  account  of  the  fact,  how- 
ever, that  milk  as  discharged  from  the  heater 
flowed  first  into  a  tank  from  which  the  various 
holding  tanks  were  filled,  and  on  account  of  the 
added  fact  that  when  these  tanks  were  discharging 
218 


FROM    THE    PRACTICAL    VIEWPOINT 

the  milk,  it  flowed  into  a  second  tank  before  being 
conveyed  to  the  cooling  apparatus,  it  is  probable 
that  the  milk  was  actually  held  at  the  highest  tem- 
perature for  a  period  of  at  least  twenty-seven 
minutes. 

A  sample  was  taken  from  the  raw  milk  before 
being  clarified.  This  milk,  upon  setting,  was  found 
to  contain  15  per  cent,  of  cream  and  to  have  a  fat 
content  of  3.9  per  cent.  A  second  sample  was 
taken  from  milk  which  had  been  heated  to  145° 
F.,  and,  after  holding,  was  set  and  found  to  con- 
tain lOi/2  per  cent,  cream  and  3.9  per  cent,  butter 
fat.  A  third  sample  was  taken  from  milk  which 
was  heated  to  144°,  and  was  found  to  contain  8 
per  cent,  of  cream  and  3.9  per  cent,  butter  fat.  A 
fourth  sample  was  taken  from  milk  which  was 
heated  to  142°,  and  was  found  to  have  a  cream 
content  of  8  per  cent,  and  3.9  per  cent,  butter  fat. 

These  results  indicated  that  the  milk  which  was 
heated  to  145°  contained  a  greater  percentage  of 
cream,  by  volume,  than  that  which  was  heated  to 
142°.  The  reason  for  this  was  not  apparent.  The 
milk  pasteurized  at  this  plant  was  received  from 
the  railroad  in  cans  which  had  been  shipped  from 
the  country.  The  milk  was  dumped  from  these 

219 


THE    PASTEURIZATION    OF    MILK 

cans  into  a  large  dump  vat,  from  which  it  was 
pumped  to  a  receiving  vat  upon  the  second  floor 
and  was  thence  allowed  to  flow  through  a  clarifier, 
from  which  it  was  discharged  into  a  large  mixing 
vat  and  thence  flowed  directly  to  the  milk  heater. 

FIFTH  TEST. — This  test  was  made  at  a  plant  at 
which  the  milk  was  pasteurized  by  means  of  a 
heater  somewhat  similar  to  that  shown  in  Fig.  3. 
The  holder  was  like  Fig.  21.  In  this  heater  the 
milk  is  forced  between  two  water-heated  cylin- 
ders, in  one  of  which  the  water  was  at  a  tempera- 
ture of  165°,  and  in  the  other  of  which  the  tem- 
perature of  the  water  was  nearly  at  the  boiling 
point.  The  milk,  while  being  heated,  was  kept  in 
agitation  by  means  of  a  revolving  arm,  which  was 
so  arranged  that  it  moved  between  the  two  heat- 
ing surfaces.  The  milk,  after  heating,  was  held 
in  a  series  of  eight  water- jacketed  tanks,  the  water 
surrounding  the  tanks  being  kept  at  a  temperature 
of  from  145°  to  150°  F.  The  milk,  while  in  this 
holding  tank,  was  kept  in  agitation  by  means  of  re- 
volving metal  stirrers. 

A  sample  was  first  taken  from  one  of  the  hold- 
ing tanks  in  which  the  milk  was  heated  to  a  tem- 
perature of  143°  F.  and  held  there  for  thirty 
220 


FROM    THE    PRACTICAL    VIEWPOINT 

minutes.  This  sample,  when  set,  was  found  to 
have  1 1  per  cent,  of  cream  in  volume,  and  the  but- 
ter fat  content  was  3.7  per  cent.  A  second  sample 
was  taken  from  a  holding  tank  in  which  milk  had 
been  heated  to  a  temperature  of  147°  and  held 
for  thirty  minutes,  the  temperature  of  the  milk  at 
its  discharge  being  146°.  This  milk  showed  4  per 
cent,  of  cream  and  a  fat  content  of  3.8  per  cent. 
A  third  sample  was  taken  from  a  tank  in  which 
milk  was  heated  to  145°  and  held  for  thirty 
minutes.  This  milk,  when  set,  showed  7  per  cent, 
of  cream  and  3.7  per  cent,  butter  fat.  A  fourth 
sample  was  taken  from  milk  which  had  been  heated 
to  146°  and  held  for  thirty  minutes.  This  milk 
showed  3  per  cent,  of  cream  and  3.9  per  cent,  but- 
ter fat. 

These  results  indicate  that  with  this  form  of  ap- 
paratus the  cream  line  was  seriously  interfered 
with,  even  at  a  temperature  as  low  as  143°.  The 
milk,  as  received  in  this  plant,  was  poured  from 
cans  into  a  receiving  tank  upon  the  upper  floor 
of  the  building  from  which  it  flowed  to  an  appa- 
ratus on  the  floor  below  in  which  it  was  preheated 
to  60°  F.  It  then  passed  through  centrifugal 
clarifiers  from  which  it  was  discharged  into  a  large 
221 


THE    PASTEURIZATION    OF    MILK 

tank  upon  the  receiving  floor.  From  this  tank  it 
flowed  by  gravity  to  the  pasteurizers  on  the  floor 
below. 

SIXTH  TEST. — This  test  was  made  at  a  plant  in 
which  the  milk  was  heated  by  means  of  an  appa- 
ratus shown  in  Fig.  11,  where  the  milk  is  heated 
by  means  of  what  is  known  as  a  Multitube  Heater. 
In  this  form  of  heater  a  series  of  large  tubes  are 
so  arranged  that  several  smaller  tubes  extend 
through  them.  The  milk  is  forced  through  the 
inner  tubes,  while  hot  water  is  forced  through  the 
large  surrounding  tubes.  After  heating,  the  milk 
is  discharged  into  a  series  of  eight  holding  tanks 
similar  to  those  described  in  test  No.  5.  The  water 
which  is  used  to  heat  the  milk  in  this  apparatus  is 
itself  heated  in  a  tank  outside  of  the  milk  heater 
and  is  kept  at  a  temperature  varying  between  144° 
and  163°,  the  temperature  rarely  exceeding  154°. 
From  this  tank  the  water  is  pumped  to  the  milk- 
heating  apparatus. 

The  conditions  at  this  plant  were  apparently  fa- 
vorable for  securing  good  results.  The  fact  that 
the  temperature  of  the  heating  water  was  carefully 
controlled,  made  it  impossible  to  superheat  or 
scorch  any  of  the  milk.  The  first  sample  of  milk 

222 


FROM    THE    PRACTICAL    VIEWPOINT 

was  taken  from  raw  milk  before  it  was  clarified. 
This  sample,  when  set,  showed  131/2  per  cent,  of 
cream  and  3.4  per  cent,  butter  fat.  The  second 
sample  was  taken  from  one  of  the  holding  tanks 
in  which  the  milk  was  heated  to  a  temperature  of 
146°  and  held  thereafter  for  thirty  minutes.  This 
sample,  when  set,  showed  no  cream  whatever  on 
the  cream  gauge,  the  fat  being  evidently  evenly 
distributed  throughout  the  entire  body  of  the  milk. 
This  milk  contained  3.5  per  cent,  of  butter  fat. 
A  third  sample  was  taken  from  one  of  the  holding 
tanks  in  which  the  milk  was  heated  to  143°  F. 
and  held  for  thirty  minutes.  This  milk  showed, 
upon  standing,  10  per  cent,  of  cream  and  3.7  per 
cent,  butter  fat.  Sample  No.  4  was  taken  from  a 
tank  in  which  the  milk  was  heated  to  146°  F.  and 
held  for  thirty  minutes.  This  sample  showed  5 
per  cent,  of  cream  and  3.35  per  cent,  butter  fat. 

The  results  here  obtained  indicate  that  with  this 
apparatus  if  the  milk  was  heated  above  143°  the 
cream  would  be  seriously  affected. 

SEVENTH  TEST. — A  test  was  made  at  still  an- 
other plant  in  which  the  milk  was  heated  by  means 
of  the  pasteurizer  shown  in  Fig.  9-  In  this  appa- 
ratus the  milk  is  forced  through  a  series  of  pipes 
223 


THE    PASTEURIZATION    OF    MILK 

which  are  enclosed  in  a  large  chamber  which  is 
filled  with  hot  water.  The  apparatus  somewhat 
resembles  the  tubular  boiler.  After  heating,  the 
milk  is  held  in  three  upright  cylindrical  Park  hold- 
ing tanks,  the  milk  passing  through  the  entire  se- 
ries. In  this  holding  apparatus  tests  previously 
made  indicated  that  milk  is  held  for  from  thirty- 
five  to  forty  minutes. 

In  making  this  test,  the  first  sample  was  taken 
from  the  raw  milk.  This  sample,  when  set,  showed 
14  per  cent,  of  cream  and  3.8  per  cent,  butter  fat. 
A  second  sample  was  taken  from  milk  which  was 
heated  to  a  temperature  of  143°  and  held  for  from 
thirty-five  to  forty  minutes.  This  sample,  when 
set,  showed  14  per  cent,  of  cream  and  3.8  per  cent, 
butter  fat.  In  order  to  vary  the  experiment  the 
temperature  of  the  milk  entering  the  holder  was 
then  raised  to  145°,  at  which  temperature  the  milk 
was  maintained  until  the  process  of  pasteurizing 
was  completed  for  the  day.  The  milk  in  the  filled 
holding  tanks  was  allowed  to  stand  for  thirty 
minutes  and  a  sample  was  taken  from  that  which 
was  being  discharged  from  the  holding  tank,  which 
showed,  on  standing,  14  per  cent,  of  cream  and 
3.85  per  cent,  butter  fat.  A  fourth  sample  was 
224 


FROM    THE    PRACTICAL    VIEWPOINT 

taken  from  the  milk  which  was  last  discharged 
from  the  holder.  This  milk  had  been  in  the  holder 
for  exactly  sixty  minutes.  Upon  standing,  this 
milk  showed  9  per  cent,  of  cream  and  3.7  per  cent, 
butter  fat. 

These  results  indicated  that  milk  could  be  heated 
to  145°  and  held  for  thirty  minutes  without  any 
injurious  effect  upon  the  cream  line  being  pro- 
duced, but  that  if  the  milk  was  held  for  an  hour, 
the  cream  line  was  considerably  affected. 

EIGHTH  TEST. — A  further  test  was  made  at  a 
pasteurizing  plant  in  which  the  milk  was  heated 
by  means  of  the  heater  shown  in  Fig.  7,  and  held 
in  the  holder  illustrated  in  Fig.  27-  In  this  appa- 
ratus the  milk  is  forced  through  a  series  of  pipes 
which  are  themselves  enclosed  in  a  larger  pipe 
through  which  hot  water  is  forced.  The  holding 
apparatus  consists  of  a  series  of  large  tubes 
through  which  the  milk  is  allowed  to  flow.  It  re- 
quires about  thirty-five  minutes  for  the  milk  to  be 
discharged  through  the  holding  tubes. 

A  sample  was  taken  from  the  raw  milk,  before 
clarifying.  This  was  found  to  contain  !5l/2  per 
cent,  of  cream  and  3.5  per  cent,  butter  fat.  A  sec- 
ond sample  was  taken  from  milk  which  had  been 
225 


THE    PASTEURIZATION    OF    MILK 

clarified,  and  this  was  found  to  contain  12  per  cent, 
cream  and  3.6  per  cent,  butter  fat,  there  being  an 
apparent  reduction  of  3^/2  per  cent,  of  cream  vol- 
ume due  to  the  clarifying  process.  A  third  sam- 
ple was  taken  from  milk  leaving  the  holder  at  a 
temperature  of  142°.  This  was  found  to  contain 
8  per  cent,  cream  and  3.7  per  cent,  butter  fat.  A 
fourth  sample  was  taken  from  milk  leaving  the 
holder  at  a  temperature  of  145°.  This  showed  7 
per  cent,  of  cream  and  3.6  per  cent,  butter  fat. 

The  results  here  obtained  indicated  that  milk 
which  is  heated  to  145°  shows  about  the  same 
amount  of  cream,  by  volume,  as  that  which  is 
heated  to  142°,  but  the  milk  heated  to  either  tem- 
perature showed  but  little  more  than  half  the 
amount  of  cream  which  was  found  in  the  raw 
milk. 

The  milk  at  this  plant  was  received  in  the 
dumping  tank  on  the  first  floor,  from  which  it  was 
pumped  to  a  tank  upon  the  pasteurizing  floor,  and 
thence  flowed  through  a  centrifugal  clarifier  into 
the  mixing  tank.  From  this  tank  it  was  pumped 
through  the  heater  and  holder,  and  after  being 
discharged  from  the  holder  was  again  pumped 
through  the  cooler. 

226 


FROM    THE    PRACTICAL    VIEWPOINT 

Summary   of  Results 

All  the  tests  made  indicate  that  when  milk  is 
cleaned  by  a  centrifugal  clarifier,  the  volume  of 
cream  in  the  milk  suffers  a  reduction  of  2  per  cent, 
to  3  per  cent. 

The  number  of  tests  made  was  probably  not 
sufficient  to  warrant  the  drawing  of  absolutely 
definite  conclusions.  It  was  evident,  however,  that 
the  volume  of  cream  in  bottled  milk  was  influenced 
by  various  factors,  some  of  which  are  apparently 
little  understood.  These  factors  include: 

(1)  The    temperature    to    which    the    milk    is 
heated. 

(2)  The  length  of  time  for  which  milk  is  held 
at  the  high  temperature. 

(3)  The    temperature    of    the    heating    medium 
with  which  the  milk  comes   in  contact  during  the 
heating  process. 

(4)  The  clarification  of  the  milk. 

(5)  The  type  of  apparatus  used  in  treating  the 
milk. 

(6)  The  amount  of  agitation  to  which  the  milk 
is  subjected,  especially  while  hot. 

This   last   factor   has   a   greater   influence   upon 

227 


THE    PASTEURIZATION    OF    MILK 

the  cream  line  than  is  ordinarily  appreciated.  It 
lias  been  stated  to  the  writer,  that  in  one  instance 
where  the  cream  line  was  materially  reduced  dur- 
ing the  pasteurization  process,  the  experiment  was 
made  of  reducing^the  speed  of  the  agitator  which 
kept  the  hot  milk  in  motion.  After  the  speed  had 
been  so  reduced  it  was  found  that  the  cream  line 
upon  the  milk  resumed  its  normal  character. 

It  will  also  be  noted  from  the  foregoing  descrip- 
tion of  the  various  methods  of  handling  milk  that 
in  those  plants  where  there  was  most  agitation  of 
the  milk,  and  especially  where  the  pumping  of 
hot  milk  was  practiced,  the  most  difficulty  with  the 
cream  line  was  experienced.  There  are  possibly 
other  factors  which  affect  the  cream  line,  among 
which  may  be: 

1st,  the  age  of  the  milk  before  pasteurization. 

2nd,  the  grade  of  cows  from  which  the  milk  was 
produced. 

3rd,  the  fact  that  milk  has  or  has  not  been  frozen 
before  being  treated. 

The  tests  made  proved  that  it  is  entirely  pos- 
sible, under  the  most  favorable  conditions,  to  heat 
milk  to  145°  and  hold  it  for  thirty  minutes  without 
producing  any  injurious  effect  upon  the  cream  line. 
228 


FROM    THE    PRACTICAL    VIEWPOINT 

It  is  also  doubtless  true,  however,  that  with  some 
types  of  apparatus  in  use  by  the  milk  dealers  and 
with  some  conditions  under  which  milk  is  handled, 
a  real  difficulty  is  experienced  in  obtaining  satis- 
factory results. 

The  chart  shown  in  Fig.  34,  drawn  by  Dr.  North, 
indicates  graphically  the  temperatures  and  holding 
times  within  which  it  is  safe  to  heat  milk  without 
affecting  the  cream  line.  Such  a  chart  cannot  show 
the  other  factors  which  also  affect  the  results,  such 
as  the  amount  of  agitation,  etc. 

If  the  milk  is  being  heated  and  an  attempt  is 
made  to  keep  the  milk  at  a  temperature  no  lower 
than  145°  F£  it  is  almost  certain  that  the  tempera- 
ture will  at  times  reach  from  146  to  148°  or  higher,, 
and  that  it  will  at  times  be  held  longer  than  thirty 
minutes.  It  is  almost  mechanically  impossible  to 
so  control  the  temperature  of  milk  while  heating 
that  there  will  not  be  considerable  variation. 

The  agitation  probably  has  the  effect  of  break- 
ing up  the  fat  globules  into  smaller  masses.  Since 
each  globule  of  fat  is  surrounded  with  a  film  of 
casein  or  skim  milk,  which  is  heavier  than  the  fat,  it 
is  evident  that  as  the  mass  of  fat  becomes  smaller, 
the  proportional  amount  of  the  surrounding  skim 

229 


THE    PASTEURIZATION    OF    MILK 


TIME.     AND    TE.MPLRATURE.     FOR 
MILK    PASTEURIZATION. 


iO  20  30 

Tl  ME.   IN   MINUTE.5 

FIG.  34 

230 


FROM    THE    PRACTICAL    VIEWPOINT 

milk  becomes  greater,  till  we  reach  a  point  when 
the  buoyant  fat  cannot  lift  the  heavier  envelope, 
and  our  balloon  of  fat  stays  down. 

Just  why  the  high  heat  and  the  long  holding 
scatters  the  fat  permanently  through  the  body  of 
the  milk  is  not  so  clear.  It  may  be  due  to  chemical 
changes  which  occur. 

In  the  pasteurizing  equipment  described  on 
pages  124  and  131  it  is  claimed  that  the  superheat- 
ing of  the  held  milk  has  a  beneficial  effect  upon 
the  cream  lines. 

The  tables  following  show  graphically  the  re- 
sults of  the  tests  made.  They  indicate  the  varied 
conditions  under  which  milk  was  handled  in  the 
various  tests  and  the  percentage  of  the  cream  upon 
each  sample  as  well  as  the  percentage  of  butter  fat 
which  was  determined  by  the  Babcock  test. 


231 


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239 


J 


CONCLUSION 


In  conclusion,  it  may  not  be  amiss  to  say  that  all 
the  indications  lead  to  the  conviction  that  the  pas- 
teurization of  milk  is  not,  as  some  have  claimed,  a 
fad.  It  is  coming  more  and  more  into  use,  as  a 
recognized  sanitary  measure,  which  is  at  present 
necessary.  Whether  a  time  may  come  when  it  will 
be  safe  for  large  communities  to  consume  their 
milk  unheated  is  a  question  which  at  present  is  not 
a  subject  for  practical  consideration.  The  South 
and  West,  which  have  been  slow  to  recognize"  the 
value  of  pasteurization,  are  coming  into  line,  and 
the  teaching  of  practical  methods  of  handling  ap- 
paratus used  in  pasteurizing  milk  is  a  wise  thing 
for  the  dairy  schools  to  take  up.  Practical  meth- 
ods of  controlling  the  actual  operation  of  pasteuriz- 
ing plants  should  be  taught,  and  instruction  should 
be  available  for  inspectors  employed  by  munici- 
palities, as  well  as  for  those  who  are  to  become 
such  inspectors,  in  order  that  they  may  be  equipped 
to  render  the  most  useful  service  to  the  com- 
munities when  they  assume  their  duties. 
240 


THE    PASTEURIZATION    OF    MILK 

Other  methods  may  be  discovered  by  whicli  milk 
may  be  rendered  safe  with  less  trouble  and  ex- 
pense, but  none  such  are  now  in  sight,  and  until 
they  appear  our  towns  and  cities  must  depend  upon 
the  proper  application  of  heat  to  render  milk  safe 
as  food. 

It  is  due  to  the  citizens  that  the  actual  treatment 
of  the  milk  be  so  intelligently  supervised  and  con- 
trolled that  it  will  in  reality  be  as  safe  as  the 
people  have  a  right  to  expect. 


241 


INDEX 


Adulteration  of  Milk    5,  6 

Agricultural   Department 2 

Ahlborn 11 

Air-compressors 135 

Ayers   (and  Johnson)    9,  86,  155 

B 

Boards  of  Food  Control 2 

Bottle-capping    177-180 

Bottle-cleaning 168-175 

Bottle-filling    176 

Bottles,    Paper    180-182 

Bovine  Tuberculosis   1 8-22 

C 

Capping  Bottles   177-180 

Chemical   Changes    27 

Cleaning  and  Clarifying 150—155 

Color    Test    115,116 

Compressed  Air    135 

Conclusion    240 

243 


INDEX 


PAGE 

Containers,  Washing  of 163-175 

Control    (Official)    of   Pasteurization 32-34 

Controllers,  Temperature    27,   133-140 

Cooling    155 

Coolers,  Open   155-160 

Tank    160-161 

Tubular    162 

Cream  Line 21,  29,  208-239 

D 

Department  of  Health,  Reprints 9 

New  York  City 27,  43,  94,  209 

Denmark    11,    12 

E 

Efficiency  of  Apparatus 185-207 

Electric  Process    90,    91 

Enzymes    30 

F 

Filling  Bottles    1 76 

Fresca    11 

0 

Geneva  Experiment  Station 19,  158 


INDEX 


H 

PAGE 

Health  Department 2 

New  York  City 9,  27,  43,  94,  209 

Heaters    43 

First   Type    44-47 

Second    Type    47-56 

Third   Type    56-65 

Fourth  Type 65-77 

Fifth  Type   77-89 

Holding  Time,  Method  of  Calculation...    96,103 

Holders 94-107 

Absolute   Type    94-1 1 1 

Points  to  be  Observed  in 108,  109 

Continuous  or  Flow  Type 111-132 

Disturbances  of  Holding  Time.  .113, 114 

Horizontal    Tank    124-126 

Park   Tank    111-123 

Testing  of  Holding  Time 115,  116 

Tubular    126-129 

Home  Pasteurization    183,  184 

I 

Infection  of  Milk 4,  5,  18-22 

245 


INDEX 


J  PAGE 

Jacob!     13 

Johnson    9,  86,   155 

K 
Knlp    158 

M 

Milk  Dealers'  Organizations   6,  7 

Milk,  Changes  Due  to  Pasteurization.  ...  27 

Methods  of  Official  Control 32-34, 

N 
New  York  City 9,   15,  27,  43,  94,  209,  212 

O 

Ozone  Treatment    92 

P 

Park 20,  23,   111 

Pasteur     10 

Paper  Bottles    1 80-1 82 

246 


INDEX 


PAGE 

Pasteurization  in  General    1—42 

Pasteurization    Literature    7~9 

Pasteurization,    Home    183,  184 

Regulations    27 

Pasteurized  Milk,  Requirements  for  Secur- 
ing Good  Results    31,  32 

Pasteurizer,  Danish    11,  12 

Pasteurizing  Plant,  Requirements  for  Sat- 
isfactory Equipment 36-42 

Pasteurizing  in  Vacuum  Pans 89,  90 

Percentage  of  Bacterial  Reduction 185-207 

Public  Health  Reports 18 

Pumps    39 

R 

Recorders — Temperature 140-149 

Reid    11 

Rosenau,  M.  J 9,  22,  23,  25,   183 

Ruehl  (and  Kulp)    158 

S 

Schores 25,  27 

Septic  Sore  Throat 17,  18 

Sheele    10 

247 


INDEX 


PAGE 

Sohxlet 13 

Storch  Test 32 

Superheating  of  Milk 131 

T 

Temperature  Controller    27,  133-14-0 

Temperature    Test,    Holding    Tanks 115,  116 

Temperature  Recorders    140-14-9 

Testing  Cleaned  Containers    174,  175 

Testing  of  Holding  Time    1 15,  116 

Thermal  Death  Point 27 

Tuberculosis   12,  18-21 

Typhoid  Fever   17 

U 

Ultra  Violet  Rays 92 

V 

Vacuum  Pans    89, 90 

W 

Washing  of  Containers    163-175 

Winslow 18 

248 


PRINTERS 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN     INITIAL     FINE     OF     25     CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


&  1933 

SEP  20  .934 

APR  251936 
APR  10 1941 M 


JAN  13 1954  LU 
78  W  v" 


D|EC  2JJM99ftl995 
CIRCULATION  DEPT. 


358832 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


